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Things A Boy Should 

Know About 

Ele6lricity 



BY 



THOMAS M. ST. JOHN, Met. E. 

Author of ** Fun With Magnetism," " Fun With Electricity, 
" How Two Boys Made Their Own Electrical Appa- 
ratus," "The Study of Elementary Electricity 
and Magnetism by Experiment," etc. 




NEW YORK 

THOMAS M. ST. JOHN 

407 West 51st Street 
1900 



68283 

OCT 30 1900 

CopyngM entry 

StCf "»)P COPY. 
OHOt K D'ViSION. 

OCT 31 I90U 



Copyright, 1900, 
By Thomas M. St. John. 



V'-^ 



THINGS A BOY SHOULD KNOW 
ABOUT ELECTRICITY 



TABLE OF CONTENTS 

Chapter Page 

I. About Frictional Electricty. . . . . 7 

II. About Magnets and Magnetism ... 21 

III. How Electricity is Generated by the Voltaic Cell, 32 

IV. Various Voltaic Cells, . . . -3^ 
V. About Push-Buttons, Switches and Binding-Posts, 43 

VI. Units and Apparatus for Electrical Measurements, 48 
VII. Chemical Effects of the Electric Current, . 58 
VIII. How Electroplating and Electrotyping are Done, . 60 
IX. The Storage Battery, and How it Works, . 63 
X. How Electricity is Generated by Heat, . . 68 
XI. Magnetic Effects of the Electric Current, . 71 
XII. How Electricity is Generated by Induction, . 77 
XIII. How the Induction Coil Works, ... 80 
XIV. The Electric Telegraph, and How it Sends Mes- 
sages, ...... 84 

XV. The Electric Bell and Some of its Uses, . . gi 

XVI. The Telephone and How it Transmits Speech, 95 

XVII. How Electricity is Generated by Dynamos, . loi 

XVIII. How the Electric Current is Transformed, . 109 

XIX. How Electric Currents are Distributed for Use, . 114 

XX. How Heat is Produced by the Electric Current, 124 

XXI. How Light is Produced by the Incandescent Lamp, 129 

XXII. How Light is Produced by the Arc Lamp, . 135 

XXIII. X-Rays, and How the Bones of the Human Body 

are Photographed, ..... 141 

XXIV. The Electric Motor, and How it Does Work, . 147 
XXV. Electric Cars, Boats and Automobiles, . . 154 

XXVI. A Word About Central Stations, . . 162 

XXVII. Miscellaneous Uses of Electricity, . . . 165 



TO THE READER 



For the benefit of those who wish to make their own 
eledlrical apparatus for experimental purposes, references 
have been made throughout this work to the "Apparatus 
Book; " by this is meant the author's '' How Two Boys 
Made Their Own EleArical Apparatus." 

For those who wash to take up a course of elementary 
eledlrical experiments that can be performed with simple, 
home-made apparatus, references have been made to 
'' Study; " by this is meant "The Study of Elementary 
Eledlricity and Magnetism by Experiment." 

The Author. 



Things A Boy Should Know About 
Electricity 



CHAPTER I. 

ABOUT FRICTIONAL ELECTRICITY. 

I. Some Simple Experiments. Have you ever 
shuffled your feet along over the carpet on a winter's 
evening and then quickly touched your finger to the 
nose of an unsuspedling friend? Did 
he jump when a bright spark leaped 
from your finger and struck him fairly 
on the very tip of his sensitive nasal 
organ ? 

Did you ever succeed in proving to 
the pussy-cat, Fig. i, that something 
unusual occurs when you thoroughly 
rub his warm fur with your hand ? Did 
you notice the bright sparks that passed 
to your hand when it was held just above 
the cat's back? You should be able to 
see, hear, and feel these sparks, especially when the air 
is dry and you are in a dark room. 

Did you ever heat a piece of paper before the fire until 
it was real hot, then lay it upon the table and rub it from 
end to end with your hand, and finally see it cling to the 
wall? 




8 



ABOUT FRICTION AI. KI^ECTRICITY. 



Were you ever in a factory where there were large 
belts running rapidly over pulleys or wheels, and where 
large sparks would jump to your hands when held near 
the belts? 

If you have never performed any of the four experi- 
ments mentioned, you should try them the first time a 
chance occurs. There are dozens of simple, fascinating 
experiments that may be performed with this kind of 
eledlricity. 

2. Name. As this variety of eledlricity is made, or 
generated, by the friclion of substances upon each other, 
it is Qdll^di frUlional eledlricity. It is also called static 
electricity, because it generally stands still upon the sur- 
face of bodies and does not '' flow in currents " as easily 
as some of the other varieties. Static eledlricity may be 

produced by induction 
as well as by fridlion. 
3. History. It has 
been known for over 
2 ,000 3'ears that certain 
substances adt queerly 
when rubbed. Amber 
was the first substance 
upon which ele(ftricity 
was produced by fric- 
tion, and as the Greek 
name for amber is 
elektron, bodies so affedled were said to be eleflrtjied. 
When a body, like ebonite, is rubbed with a flannel 
cloth, we say that it becomes charged with electricity. 
Just what happens to the ebonite is not clearly under- 




ABOUT FRICTIONAL EI.ECTRICITY. 



sr 



stood. We know, however, that it will attrac5l light 
bodies, and then quickly repel them if they be condudtors. 
Fig. 2 shows a piece of tissue-paper jumping toward a 
sheet of ebonite that has been elec?trified with a flannel 
cloth. 

4. Conductors and Non-Conductors. Electricity 
can be produced upon glass and ebonite because they do 
not carry or conduct it away. If a piece of iron be 
rubbed, the eledlricity passes from the iron into the 
earth as fast as it is generated, because the iron is a con- 
du5lor of eledlricity. Glass is an msidator or no7i-co7t' 
du5lor. Fridlional eledlricity resides upon the outside, 
only, of condudlors. A hollow tin box 

will hold as great a charge as a solid 
piece of metal having the same out- 
side size and shape. When fridlional 
eledlricity passes from one place to 
another, sparks are produced. Light- 
ning is caused by the passage of 
static eledlricity from a cloud to the 
earth, or from one cloud to another. 
In this case air forms the condudlor. 
(For experiments, see ''Study," 
Chapter VII.) 

5. Electroscopes. A piece of carbon, pith, or even 
a small piece of damp tissue-paper will serve as an eledlro- 
scope to test the presence of static eledlricity. The pith 
is usually tied to a piece of silk thread which is a non- 
condudlor. Fig. 3 shows the ordinary form of pith-ball 
electroscope. 

The leaf electroscope is a very delicate apparatus. Gold- 




Fig. 3- 



lO 



ABOUT FRICTIONAL ELECTRICITY. 



leaf is generally used, but aluminum-leaf will stand 
handling and will do for all ordinary purposes. Fig. 4 
shows a common form, the glass being used to keep 
currents of air from the leaves and at the same time to 
insulate them from the earth. 

Eledlroscopes are used to show the presence, relative 

amount, or kind of static 
eledlricity on a body. 
(See ^' Study," Chapter 
XL) 

6. Two Kinds of 
Electrification. It can 
be shown that the eledlri- 
fication produced on all 
bodies by fric5lion is not 
the same; for example, 
that generated with glass 
and silk is not the same 
as that made with ebonite 
and flannel. It has been 
agreed to call that pro- 
duced by glass and silk 
positive, and that by 
ebonite and flannel nega- 
tive. The signs + and — are used for positive and 
negative. 

7. Laws of Electrification, (i) Charges of the 
same kind repel each other; (2) charges of unlike kinds 
attradl each other; (3) either kind of a charge attradls 
and is attracted by a neutral body. 

8. Static Electric Machines. In order to produce 




ABOUT FRICTIONAL ELECTRICITY. II 

static eledlricity in quantities for experiments, some 
device is necessary. 

The eleSlrophorus (e-lec-troph'-o-rus) is about the sim- 
plest form of machine. Fig. 5 shows a simple eleclroph- 
orus in which are two insulators and one conducT:or. 
The ebonite sheet E S is used with a flannel cloth to gen- 
erate theelecftricity. The metal cover E C is lifted by the 
insulating handle E R. The cover E C is placed upon 
the thoroughly charged sheet E S, and then it is touched 
for an instant with the finger, before lifting it by E R. 
The charge upon E C can then be 
removed by bringing the hand near 
it. The bright spark that passes 
from E C to the hand indicates that 
E C has discharged itself into the 
earth. The a6lion of the eledlroph- 
orus depends upon inducftion. (For 
experiments, details of adlion, 
induced elecftrification, etc., see 
' ' The Study of Elementary Elec?tricity and Magnetism 
by Experiment," Chapters VIII. and IX.) 

The first ele5lric viachine consisted of a ball of sulphur 
fastened to a spindle which could be turned by a crank. 
By holding the hands or a pad of silk upon the revolving 
ball, eledlricity was produced. 

9. The Cylinder Electric Machine consists, as 
shown in Fig. 6, of a glass cylinder so mounted that it 
can be turned by a crank. Fricftion is produced by a 
pad of leather C, which presses against the cylinder as it 
turns. Ele6lric sparks can be taken from the large * ' con- 
dudlors ' ' which are insulated from the earth. The oppo- 




12 



ABOUT FRICTIONAI, EL,ECTRICITY. 




Fig. 6. 




Fig. 7. 



ABOUT FRICTIONAL ELECTRICITY. 



13 



site eledlricities unite with sparks across D and E. If 
use is to be made of the eledlricity, either the rubber or 
the prime condudlor must be connedled with the ground. 
In the former case positive eledlricity is obtained; in the 
latter, negative. 

10. The Plate Electrical Machine. Fig. 7 also 
shows an old form of machine. Such machines are made 
of circular plates of glass or ebonite, two rubbing pads 




Fig. 8. 

being usually employed, one on each side of the plate. 
One operator is seen on an insulated stool (Fig. 7), the 
ele(5lricity passing through him before entering the earth 
by way of the body of the man at the right. 

II. The Toepler-Holtz Machine, in one form, is 
shown in Fig. 8. The eledlricity is produced by the 
principle of indudlion, and not by mere fridlion. This 
machine, used in connection with condensers, produces 
large sparks. 



14 



ABOUT FRICTIONAI. EI.ECTRICITY. 




12. The Wimshurst Machine is of recent date, and 
not being easily aflfedled by atm(5spheric changes, is very 
useful for ordinary laboratory work. Fig. 9 shows one 

form of this machine. 

13. Influence Machines 
for Medical Purposes are 
made in a large variety of 
forms. A Wimshurst machine 
is generally used as an exciter 
to charge the plates of the 
large machine when they lose 
their charge on account of 
excessive moisture in the 
atmosphere. Fig. 10 shows a 
large machine. 

14. Uses of Electrical 
Machines. Static elecflricity has been used for many 
years in the labora- 
tory for experi- 
mental purposes, for 
charging condensers, 
for medical pur- 
poses, etc. It is 
now being used for 
X-ray work, and 
considerable ad- 
vancement has been 
made within a few 
years in the construc- 
tion and efficiency 
of the machines. 




ABOUT FRICTIONAI. EI.ECTRICITY. 



15 



With the modern machines large sparks are produced 
by merely turning a crank, enough eledlricity being pro- 
duced to imitate a small thunderstorm. The sparks of 
home-made lightning will jump several inches. 

Do not think that elecftricity is generated in a com- 
mercial way by static eledlric machines. The prac?tical 
uses of static eledlricity are very few when compared 
with those of current elecftricity from batteries and 
dynamos. 

15. Condensation of Static Electricity. By means 





Fig. II. 



Fig. 12. 



of apparatus called condensers, a terrific charge of static 
eledlricity may be stored. Fig. 11 shows the most 
common form of condenser, known as the Leydeii jar. 
It consists of a glass jar with an inside and outside coating 
of tin-foil. 

To charge the jar it is held in the hand so that the out- 
side coating shall be connected with the earth, the sparks 



i6 



ABOUT FRICTIONAI. K1.ECTRICITY. 



from an eledlric machine being passed to the knob at the 
top, which is connedled by a chain to the inside coating* | 
To discharge the jar, Fig. 12, a condudlor with an 

insulating handle is placed 
against the outside coat ; 
when the other end of the 
condudlor is swung over 
towards the knob, a bright 
spark passes between them. 
This device is called a dis- 
charger. Fig. 13 shows a 
discharge through ether 
which the spark ignites. 

16. The Leyden Bat- 
tery, Fig. 14, consists of 
several jars connedled in such a way that the area of the 
inner and outer coatings is greatly increased. The bat- 
tery has a larger ca- 
pacity than one of its 
jars. (For Experi- 
ments in Condensa- 
tion, see ''Study,'' 
Chapter X.) 

17. Electromotive 
Force of Static 
Electricity. Al- 
though the sparks of 
static eledlricity are 





Fig. 14. 



large, the quantity of eledlricity is very small. It would 
take thousands of galvanic cells to produce a spark an 
inch long. While the quantity of static eledlricity is 



ABOUT FRICTIONAL ELECTRICITY. 




Fig. 15. 



small, its potential, or elecT:romotive force (E. M. F.), 

is very high. We say that an ordinary gravity cell has 

an E. M. F. of a little over one volt. Five such cells 

joined in the proper way 

would have an E. M. F. of a 

little over five volts. You 

will understand, then, what 

is meant when we say that the 

E. M. F. of a lightning flash 

is millions of volts. 

18. Atmospheric Elec- 
tricity. The air is usually 
eledlrified, even in clear 
weather, although its cause is 
not thoroughly understood. 
In 1752 it was proved by 

Benjamin Franklin (Fig. 15), with his famous kite 
experiment, that atmospheric and fricflional electricities 
are of the same nature. By means of a kite, the string 
being wet by the rain, he succeeded, during a thunder- 
storm, in drawing sparks, charg- 
ing condensers, etc. 

19. Lightning may be pro- 
duced by the passage of elecflricity 
between clouds, or between a 
cloud and the earth (Fig. 16), 
which, with the intervening air, 
have the effedl of a condenser. 
When the attraclion between 
the two eledlrifications gets great enough, a spark passes. 
When the spark has a zigzag motion it is called chain 




Fig. 16. 



i8 



ABOUT FRICTIONAIy KI.ECTRICITY. 



lightning. In hot weather flashes are often seen which 
light whole clouds, no thunder being heard. This is 
called heat lightnings and is generally considered to be 

due to distant dis- 
charges, the light of 
which is refledled by 
the clouds. The 
lightning flash repre- 
sents billions of volts. 

20. Thunder is 
caused by the violent 
disturbances produced 
in the air by light- 
ning. Clouds, hills, 
etc. produce echoes^ 
which, with the orig- 
inal sound, make the 
rolling effedl. 

21. Lightning- 
Rods, when well 
construdled, often pre- 
vent violent dis- 
charges. Their point- 
ed prongs at the top 
allow the negative 
eledlricity of the earth 

to pass quietly into the air to neutralize the positive in 
the cloud above. In case of a discharge, or stroke of 
lightning, the rods aid in conducting the eledlricity to 
the earth. The ends of the rods are placed deep in the 
earth. Fig. 17. 




ABOUT FRICTIONAL ELECTRICITY. 



19 



22. St. EImo*s Fire. Elecftrification from the earth 
is often drawn up from the earth through the masts of 




Fig. 18. 



ships, Fig 18, to neutralize that in the clouds, and, as it 
escapes from the points of the masts, light is produced. 
23. Aurora Borealis, also called Northern Lights, are 



20 



^BOUT FRICTIONAI. ELECTRICITY. 




Fig. 19. 



luminous effedls, Fig. 19, often seen in the north. They 
often occur at the same time with magnetic storms, when 
telegraph and telephone work ma}- be disturbed. The 
exac5l cause of this light is not known, but it is thought 
by many to be due to disturbances in the earth's mag- 
netism caused by the adlion of the sun. 



CHAPTER II. 

ABOUT MAGNETS AND MAGNETISM. 

24. Natural Magnets. Hundreds of 3'ears ago it 
was discovered that a certain ore of iron, called lodestone, 
had the power of picking up small pieces of iron. It was 
used to indicate the north and south line, and it was dis- 
covered later that small pieces of steel could be perma- 
nently magnetized by rubbing them upon the lodestone. 

25. Artificial Magnets. Pieces of steel, when mag- 
netized, are called artificial magnets. They are made in 
many forms. The electromagnet is also . an artificial 
magnet; this will be treated separately. 

26. The Horseshoe Magnet, Fig. 20, is, however, 
the one with which we are the most familiar. 
They are alw^ays painted red, but the red paint 
has nothing to do wdth the magnetism. 

The little end-piece is called the keeper, or 
armature ; it should alw^aA'S be kept in place 
when the magnet is not in use. The magnet 
itself is made of steel, w^hile the armature is 
made of soft iron. Steel retains magnetism 
for a long time, while soft iron loses it almost instantly. 
The ends of the magnet are called its poles, and nearly 
all the strength of the magnet seems to reside at the 
poles, the curved part having no attradlion for outside 
bodies. One of the poles of the magnet is marked w4th 
a line, or with the letter N. This is called the north 
pole of the magnet, the other being its south pole. 




22 ABOUT MAGNETS AND MAGNETISM. 

' 27. Bar Magnets are straight magnets. Fig. 21 




Fig. 21. 

shows a round bar magnet. The screw in the end is for 
use in the telephone, described later. 

28. Compound Magnets. When several thin steel 
magnets are riveted together, a com- 
pound magnet is formed. These can be 
made with considerable strength. Fig. 
22 shows a compound horseshoe magnet. 
Fig. 23 shows a form of compound bar 
magnet used in telephones. The use of 
the coil of wire will be explained later. 
A thick piece of steel can not be magnet- 
ized through and through. In the com- 
pound magnet we have the eflecfl of a 
thick magnet pradlically magnetized 
through and through. 

29. Magnetic and Diamagnetic 
Bodies. Iron, and substances contain- 
ing iron, are the ones most readily attracted by a magnet. 




Fig. 22. 




Fig. 23. 

Iron is said to be magnetic. Some substances, like 
nickel, for example, are visibly attracfled by very strong 



ABOUT MAGNETS AND MAGNETISM. 



23 




Fig. 24. 



magnets only. Strange as it may seem, some substances 

are adlually repelled by strong magnets; these are called 

diamagnetic bodies. Brass, copper, zinc, etc., are not 

visibly affedled by a magnet. 

Magnetism will a6l through 

paper, glass, copper, lead, 

etc. 

30. Making Magnets. 
One of the strangest proper- 
ties that a magnet has is its power to give magnetism to 
another piece of steel. If a sewing-needle be properly 
rubbed upon one of the poles of a magnet, it will be- 
come strongly magnetized 
and will retain its mag- 
netism for 3'ears. Strong 
permanent magnets are 
made with the aid of 
electromagnets. Any 
number of little magnets 
may be made from a horse- 
shoe magnet without in- 
juring it. 

31, Magnetic Needles 
and Compasses. If a 
bar magnet be suspended 
by a string, or floated 
upon a cork, which can 
easily be done wdth the 
magnet made from a sewing-needle. Fig. 24, it will 
swing around until its poles point north and south. Such 
an arrangement is called a magnetic needle. In the reg- 




Fig. 25. 



24 



ABOUT MAGNETS AND MAGNETISM. 



ular compass^ a magnetic needle is supported upon a pivot. 
Compasses have been used for many centuries by mar- 
iners and others. Fig. 25 shows an ordinary pocket 
compass, and Fig. 26 a form of mariner's compass, in 
which the small bar magnets are fastened to a card 
which floats, the whole being so mounted that it keeps a 
horizontal position, even though the vessel rocks. 




Fig. 26. 



Z2. Action of Magnets Upon Each Other. By 

making two small sewing-needle magnets, you can easily 
study the laws of attrac5lion and repulsion. By bringing 
the two north poles, or the two south poles, near each 
other, a repulsion will be noticed. Unlike poles attracft 
each other. The attracftion between a magnet and iron 
is mutual; that is, each attrac5ls the other. Either pole 
of a magnet attraAs soft iron. 



ABOUT MAGNETS AND MAGNETISM. 25 

In magnetizing a needle, either end may be made a 
north pole at will; in fadl, the poles of a weak magnet 
can easily be reversed by properly rubbing it upon a 
stronger magnet. 

33. Theory of Magnetism. Each little particle of a 
piece of steel or iron is supposed to be a magnet, even 
before it touches a magnet. When these little magnets 
are thoroughly mixed up in the steel, they pull in all 
sorts of diredlions upon each other and tend to keep the 
steel from attra(?ting outside bodies. When a magnet is 
properly rubbed upon a bar of steel, the north poles of the 
little molecular magnets of the steel are all made to point 
in the same diredlion. As the north poles help each 
other, the whole bar can attracl outside bodies. 

By jarring a magnet its molecules are thoroughly 
shaken up; in fa(5l, most of the magnetism can be 
knocked out of a weak magnet by hammering it. 

34. Retentivity. The power that a piece of steel has 
to hold magnetism is called 7'etentivity . Different kinds 
of steel have different retentivities. A sewing-needle of 
good steel will retain magnetism for years, and it is 
almost impossible to knock the magnetism out by 
hammering it. Soft steel has very little retentivit}', 
because it does not contain much carbon. . Soft iron, 
which contains less carbon than steel, holds magnetism 
very poorly; so it is not used for permanent magnets. 
A little magnetism, however, will remain in the soft iron 
after it is removed from a magnet. This is called residtial 
magnetism. 

35. Heat and Magnetism. Steel will completely 
lose its magnetism when heated to redness, and a magnet 



26 



ABOUT MAGNETS AND MAGNETISM. 



will not attradl red-hot iron. The molecules of a piece 
of red-hot iron are in such a state of rapid vibration that 
\hey: refuse to be brought into line by the magnet. 

36. Induced Magnet- 
ism. A piece of soft iron 
may be induced to become 
a magnet by holding it 
near a magnet, absolute 
contacft not being necessary. 
When the soft iron is re- 
moved, again, from the in- 
fluence of the magnet, its 
magnetism nearly all dis- 
appears. It is said to have 
temporary magnetism ; it 
had induced magnetism. If 
a piece of soft iron be held 
near the north pole of a 
magnet, as in Fig. 27, 
poles will be produced in the soft iron, the one nearest 
the magnet being the south pole, and the other the north 
pole. 

37. Magnetic Field. If a bar magnet be laid upon 
the table, and a compass be moved about it, the compass- 
needle will be attracted by 
the magnet, and it will point 
in a different direction for 
every position given to the 
compass. This strange 

power, called magnetism, reaches out on all sides of a 
magnet. The magnet may be said to a(5l by indudlion 




Fig. 27. 




Fig. 28. 



ABOUT MAGNETS AND MAGNETISM. 



27 



upon the compass-needle. The space around the magnet, 
in which this inducT:ive adlion takes place, is called the 
magnetic field. Fig. 28 shows some of the positions 













■mm 
• ■■..J, 











Fig. 29. 

taken by a compass-needle when moved about on one side 
of a bar magnet. 

38. Magnetic Figures can be made by sprinkling iron 



28 



ABOUT MAGNETS AND MAGNETISM. 



filings upon a sheet of paper under which is placed a 
magnet. Fig. 29 shows a magnetic figure made with an 
ordinary bar magnet. The magnet was placed upon the 

table and over this was laid 
a piece of smooth paper. 
Fine iron filings were sifted 
upon the paper, which was 
gently tapped so that the 
filings could arrange them- 
selves. As each particle of 
iron became a little magnet, 
by indudlion, its poles were 
attracted and repelled by 
the magnet; and when the 
paper was tapped they 
swung around to their final 
positions. Notice that the 
filings have arranged them- 
selves in lines. These lines 
show the positions of some 
of the lines of viagnetic force 
which surrounded the 
magnet. 

These lines of force pass 
from the north pole of a 
magnet through the air on 
all sides to its south pole. 

Fig. 30 shows a magnetic 
figure made from two bar 
magnets placed side by side, their unlike poles being 
next to each other. Fig. 31 shows the magnetic figure 




Fig. 31. 



ABOUT MAGNETS AND MAGNETISM. 29 

of a horseshoe magnet with round poles, the poles being 
uppermost. 

39. The Use of Armatures. A magnet attracts 
iron most strongly at its poles, because it is at the poles 
that the greatest number of lines of force pass into the 
air. Lines of force pass easily through soft iron, which 
is said to be a good conductor of them. Air is not a 
good conducfhor of the lines of force; in order, then, for 
the lines of force to pass from the north pole of a magnet 
to its south pole, they must overcome this resistance of 
the air, unless the armature is in place. A magnet will 
gradually grow weaker w^hen its armature is left off. 

40. TerrestrialMagnetism. As the compass-needle 
points to the north and south, the earth must a(5l like a 
magnet. There is a place very far north, about a thou- 
sand miles from the north pole of the earth, which is 
called the earth's north magnetic pole. Compass-needles 
point to this place, and not to the earth's real north pole. 
You can see, then, that if a compass be taken north of 
this magnetic pole, its north pole will point south. Lines 
of force pass from the earth's north magnetic pole 
through the air on all sides of the earth and enter the 
earth's south magnetic pole. The compass-needle, in 
pointing toward the north magnetic pole, merely takes 
the diredlion of the earth's lines of force, just as the par- 
ticles of iron filings arrange themselves in the magnetic 
figures. 

41. Declination. As the magnetic needle does not 
point exadlly to the north, an angle is formed between 
the true north and south line and the line of the needle. 
In Fig. 32 the line marked N S is the true north and 



30 



ABOUT MAGNETS AND MAGNETISM. 



_soutli line. The angle of variation^ or the declination, is 
the angle A between the line N S and the compass- 
needle. 

42. Dip or Inclination. If a piece of steel be care- 
fully balanced upon a support, and then magnetized, it 



s^ 



5 ^ 



Fig. 32. 



I^^ig- 33- 



will be found that it will no longer balance. The north 
pole will dip or point downward. Fig. 33 shows what 
happens to a needle when it is held in different positions 

over a bar magnet. It 
simph^ takes the diredlions 
of the lines of force as 
they pass from the ;iorth 
to the south pole of the 
magnet. As the earth's 
lines of force pass in curves 
from the north to the south 
magnetic pole, you can 
see why the magnetic 
needle dips, unless its 
south pole is made heavier 
than its north. Magnetic 
needles are balanced after they are magnetized. 

Fig. 34 shows a simple form of dipping needle. These 
are often used by geologists and miners. In the hands 




ABOUT MAGNETS AND MAGNETISM. 3 1 

of the prospedlor, the miner's compass, or dipping 
needle, proves a serviceable guide to the discovery and 
location of magnetic iron ore. In this instrument the 
magnetic needle is carefully balanced upon a horizontal 
axis within a graduated circle, and in which the needle 
will be found to assume a position inclined to the horizon. 
This angle of deviation is called the inclination or dip, 
and varies in different latitudes, and even at different 
times in the same place. 

43. The Earth's Inductive Influence. The earth's 
magnetism a(?ts inductively upon pieces of steel or iron 
upon its surface. If a piece of steel or iron, like a stove 
poker, for example, be held in a north and south line 
with its north end dipping considerably, it will be in the 
best position for the magnetism of the earth to acl upon 
it; that is, it wall lie in the diredlion taken by the earth's 
lines of force. If the poker be struck two or three times 
with a hammer to shake up its molecules, w^e shall find, 
upon testing it, that it has become magnetized. By this 
method we can pound magnetism right out of the air with 
a hammer. If the magnetized poker be held level, in an 
east and west diredlion, it wnll no longer be acled upon to 
advantage by the induflive influence of the earth, and 
we can easily hammer the magnetism out of it again. 
(For experiments on magnets and magnetism see 
''Study,'' Parti.) 



CHAPTER III. 



HOW ELECTRICITY IS 



GENERATED 
CELL. 



BY THE VOLTAIC 



44. Early Experiments. In 1786 Galvani, an 
Italian physician, made experiments to study the efTedt of 
static eledlricity upon the nervous excitability of animals, 
and especially upon the frog. He found that eledlric 

machines were not 
necessary to produce 
muscular contrac- 
tions or kicks of the 
frog's legs, and that 
they could be pro- 
duced when two dif- 
ferent metals, Fig. 
35, like iron and 
copper, for example, 
were placed in proper 
contadl with a nerve 
and a muscle anc 
then made to touch 
each other. Galvan 
first thought that th( 
frog generated the eledlricity instead of the metals. 

Volta proved that the elecftricity was caused by th* 
contac5t of the metals. He used the condensing eledlro- 
scope as one means of proving that two dissimilar metals 
become charged differently when in contacft. Volta also 




32 



HOW EI.KCTRICITY IS GENERATED. 



33 



carried out his belief by construcfting 

what is called a Voltaic Pile. He 

thought that by making several pairs 

of metals so arranged that all the 

little currents would help each other, 

a strong current could be generated. 

Fig. 36 shows 2, pile, it being made by 

placing a pair of zinc and copper discs 

in contacft with one another, then lay- 
ing on the copper disc a piece of 

flannel soaked in brine, then on top of 

this another pair, etc., etc. By con- 

nedling the first zinc and the last 

copper, quite a little current was pro- 
duced. This was a start from which 

has been built our present knowledge 

of eledlricity . Stridlly speaking, 

electricity is not generated by com- 
binations of metals or by cells; they 

really keep up a difference of potential, 

as will be seen. 

45. The Simple Cell. It has been stated that two 

different kinds of eledlrifications may be produced by 

fridlion; one positive, the other negative. Either can be 

produced, at will, by using proper mate- 
rials. Fig. 37 shows a 
secftion of a simple cell ; 
Fig. 38 shows another view. 
Cu is a piece of copper, 
and Zn a piece of zinc. 
Fig. 37. When they are placed in Fig. 38. 




Fig. 36. 





34 HOW EI.KCTRICITY IS GENERATED. 

dilute sulphuric acid, it can be shown by delicate appa- 
ratus that they become charged differently, because the 
acid adls differently upon the plates. They become 
charged by chemical adlion, and not by fridlion. The 
zinc is gradually dissolved, and it is this chemical burning 
of the zinc that furnishes energy for the eledlric current 
in the simple cell. The eledlrification, or charge, on 
the plates tends to flow from the place of higher to the 
place of lower potential, just as water tends to flow down 
hill. If a wire be joined to the two metals, a constant 
current of eledlricity wall flow through it, because the 
acid continues to ac5l upon the plates. The simple cell 
is a single-fiidd cell, as but one liquid is used in its con- 
strudlion. 

45a. Plates and Poles. The metal strips used in 
voltaic cells are called plates or eleniejits. The one most 
acfted upon by the acid is called the positive (+) plate. 
In the simple cell the zinc is the + plate, and the copper 
the negative (— ) plate. The end of a wire attached to 
the — plate is called the + pole, or eledlrode. Fig. 37 
shows the negative (— ) eledlrode as the end of the wire 
attached to the + plate. 

46. Direction of Current. In the cell the current 
passes from the zinc to the copper; that is, from the posi- 
tive to the negative plate, where bubbles of hydrogen 
gas are deposited. In the wire connedling the plates, 
the current passes from the copper to the zinc plate. In 
most cells, carbon takes the place of copper. (See 
^ ^ Study, '^ §268.) 

47. Local Currents; Amalgamation. Ordinary 
zinc contains impurities such as carbon, iron, etc., and 



HOW EI.ECTRICITY IS GENERATED. 35 

when the acid comes in contacft with thevSe, they form 
with the zinc a small cell. This tends to eat away the 
zinc without producing useful currents. The little cur- 
rents in the cell from this cause are called local currents, 
(See ''Study/* Exp. iii,§273.) This is largely over- 
come by coating the zinc with mercury. This process is 
called amalgamatio7i. It makes the zinc a(?t like pure 
zinc, which is not adled upon by dilute sulphuric acid 
when the current does not pass. (See '' Study," § 257, 

274.) 

48. Polarization of Cells. Bubbles of hydrogen gas 
are formed when zinc is dissolved by an acid. In the 
ordinary simple cell these bubbles collecft on the copper 
plate, and not on the zinc plate, as might be expecfted. 
The hydrogen is not a condu6lor of electricity, so this 
film of gas holds the current back. The hydrogen adls 
like a mr tal and sets up a current that opposes the zinc 
to the copper current. Several methods are emplo^^ed to 
get rid of the hydrogen. (See ''Study," §278, 279, 
280.) 



CHAPTER IV. 

VARIOUS VOLTAIC CELLS. 

49. Single-Fluid and Two-Fluid Cells. The sim- 
ple cell (§ 45) is a single-fluid cell. The liquid is called 
the ele£lrolyte, and this must ac5l upon one of the plates : 
that is, chemical adlion must take place in order to pro- 
duce a current. The simple cell polarizes rapidly, so 
something must be used with the dilute sulphuric acid to 
destroy the hydrogen bubbles. This is done in the 
bichromate of potash cell. 

In order to get complete depolarization — that is, to 
keep the carbon plate almost perfecftly free from hydro- 
gen, it is necessary to use two-flicid cells, or those to 
which some solid depolarizer is added to the one fluid. 

50. Open and Closed Circuit Cells. If we consider 
a voltaic cell, the wires attached to it, and perhaps some 
instrument through which the current passes, we have an 
eleHric circuit. When the current passes, the circuit is 
closed, but when the wire is cut, or in any way discon- 
nedled so that the current can not pass, the circuit is 
open or broken. (See '' Study,'' § 266.) 

Open Circuit Cells are those which can give momentary 
currents at intervals, such as are needed for bells, tel 
phones, etc. These must have plenty of time to rest, 
they polarize when the circuit is closed for a long time 
The Leclayichc and dry cells are the most common open 
circuit cells. 

Closed Circuit Cells. For telegraph lines, motors, etc., t 

36 



IP.' ■ 



\i 



VARIOUS VOLTAIC CELLS. 



37 



where a current is needed for some time, the cell must be 

of such a nature that it will not polarize quickly; it must 

give a strong and constant current. The bichromate and 
gravity cells are examples of this variety. (See ' ' Study, ' ' 

§286.) 

51. Bichromate of Potash Cells are very useful for 

general laboratory work. They are especially useful for 

operating indu(?tion coils, small 

motors, small incandescent lamps, 

for heating platinum w4res, etc. 

These cells have an E.M.F. of 

about 2 volts. Dilute sulphuric 

acid is used as the exciting fluid, 

and in this is dissolved the bi- 
chromate of potash which keeps 

the hydrogen bubbles from the 

carbon plate. (See "Apparatus 

Book," § 26.) Zinc and carbon 

are used for the plates, the -f 

pole being the ware attached to 

the carbon. 

Fig. 39 shows one form of bi- 
chromate cell. It furnishes a large quantity of current, 
I and as the zinc caii be raised from the fluid, it may be 
i kept charged ready for use for many months, and can be 
i set in adlion any time when required by lowering the 

zinc into the liquid. Two of these cells will burn a one 
, candle-power miniature incandescent lamp several hours. 
, The carbon is indestrucftible. 

Note. For various forms of home-made ceUs, see *' Apparatus 
JBook," Chapter I., and for battery fluids see Chapter II. 

I 




Fig. 39- 



38 



VARIOUS VOLTAIC CELLS. 



52. The Grenet Cell. Fig. 40 is another form of 
bichromate cell. The carbon plates are left in the fluid 
constantly. The zinc plate should be raised when the 
cell is not in use, to keep it from being uselessly dissolved. 





I 



Fig. 40. 



Fig. 41. 



53. Plunge Batteries. Two or more cells are often 
arranged so that their elements can be quickly lowered 
into the acid solution. Such a combination, Fig. 41, is- 
called a phmgc battery. The binding-posts are vSo arranged 
that currents of different strengths can be taken from the 
combination. The two binding-posts on the right of the 
battery will give the current of one cell; the two binding- 
posts on the left of the battery will give the current of 
two cells, and the two end binding-posts will give the 
current of all three cells. When not in use the elements 
must always be hung on the hooks and kept out of the ' 
solution. 



I 



VARIOUS VOLTAIC CELLS. 



39 



54. Large Plunge Batteries, Fig. 42, are arranged 
with a winch and a bar above the cells; these afford a 
ready and convenient means of lifting or lowering the 
elements and avoiding w^aste. In the battery shown, 
Fig. 42, the zincs are 4x6 inches; the carbons have the 




Fig. 42. 

same dimensions, but there are two carbon plates to each 
zinc, thus giving double the carbon surface. 

55. The Fuller Cell, Fig. 43, is another type of 
bichromate cell, used largely for long-distance telephone 
service, for telephone exchange 
and switch service, for running 
small motors, etc. It consists of a 
glass jar, a carbon plate, wdth 
proper connediions, a clay porous 
cup, containing the zinc, which is 
made in the form of a cone. A 
little mercur}^ is placed in the 
porous cup to keep the zinc well 
amalgamated. Either bichromate 
of potash or bichromate of soda can 
be used as a depolarizer. Fig. 43. 




40 



VARIOUS VOLTAIC CELLS. 







56. The Gravity Cell, sometimes called the hhiesione 
or crowfoot cell, is used largely for telegraph, police, and 
fire-alarm signal service, laboratory 
and experimental work, or whenever 
a closed circuit cell is required. The 
E.M.F. is about one volt. This is a 
modified form of the Daniell cell. Fig. 
"^ 44 shows a home-made gravity cell. 

A copper plate is placed at the 
_C bottom of the glass jar, and upon this 
rests a solution of copper sulphate 
(bluestone). The zinc plate is sup- 
ported about four inches above the 
copper, and is surrounded by a solu- 
tion of zinc sulphate which floats upon the top of the 
blue solution. An insulated wire reaches from the copper 
to the top of the cell and forms 
the positive pole. (See ' 'Appara- 
tus Book," § II to 15, for home- 
made gravity cell, its regulation, 
etc. For experiments with two- 
fluid Daniell cell, see '^ Study," 
Exp. 113, § 281 to 286.) 

56a. Bunsen Cells, Fig. 45, are 
used for motors, small incandescent 
lamps, etc. A carbon rod is in- 
closed in a porous cup, on the 
outside of which is a cylinder of 
zinc that stands in dilute sul- 
phuric acid, the carbon being in 
nitric acid. 




VARIOUS VOI.TAIC CELI.S. 



41 



57. The Leclanche Cell is an open circuit cell. Sal 
ammoniac is used as the exciting fluid, carbon and zinc 
being used for plates. Manganese dioxide is used as the 
depolarizer; this surrounds the 
carbon plate, the two being 
either packed together in a 





Fig. 46. 



Fig- 47. 



porous cup or held together in the form of cakes. The 
porous cup, or pressed cake, stands in the exciting fluid. 
The E. M. F. is about 1.5 volts. 




dK 







She mesco^ 

W BATTER? 




Fig. 48. 



42 



VARIOUS VOI.TAIC CKI.LS. 




F\g. 49. 



Fig. 46 shows a form with porous cup. The binding- 
post at the top of the carbon plate forms the + elec- 
trode, the current 
leaving the cell at this 
point. 

Tke Go7ida Prison 
Cell (Fig. 47), is a 
form of Leclanche in 
1 which the depolarizer 
is in the form of a 
cake. 

58. Dry Cells are 

open circuit cells, and 

can be carried about, 

although they are 

moist inside. The -f pole is the end of the carbon plate. 

Zinc is used as the outside case and ^ plate. Fig. 48 

shows the ordinary forms. 

Fig. 49 vshows a number of 
dry cells arranged in a box 
with switch in front, so that the 
current can be regulated at will. 
59. The Edison-Lelande 
Cells, Fig. 50, are made in 
several sizes and types. Zinc 
and copper oxide, which is 
pressed into plates, form the 
elements. The exciting fluid 
consists of a 25 per cent, solu- 
tion of caustic potash in water. 
They are designed for both open and closed circuit work. 




CHAPTER V. 

ABOUT PUSH-BUTTONS, SWITCHES AND BINDING-POSTS. 

60. Electrical Connections. In experimental work, 
as well as in the ever3'da3^ work of the electrician, elec- 
trical connecftions must constantly be made. One wire 
must be joined to another, just for a moment, perhaps, 
or one piece of apparatus must be put in an elecftric cir- 
cuit with other apparatus, or the current must be turned 
on or off from motors, lamps, etc. In order to conve- 
niently and quickly make such connedlions, apparatus 
called push-buttons, switches and binding-posts are used. 

61. Push-Buttons. The simple a(5l of pressing your 
finger upon a movable button, or knob, may ring a bell 
a mile away, or do some other equally wonderful thing. 




Fig. 51. 




"^^-^^rf. 



Fig. 52. 



Fig. 51 shows a simple push-button, somewhat like a 
simple key in const rucft ion. If we cut a wire, through 
which a current is passing, then join one of the free ends 
to the screw A and the other end to screw C, we shall be 
able to let the current pass at am- instant by pressing the 
spring B firmly upon A. 

Push-buttons are made in all sorts of shapes and sizes. 
Fig. 52 gives an idea of the general internal construdlion. 

43 



44 PUSH-BUTTONS, SWITCHES AND BINDING-POSTS. 



The current enters A by one wire, and leaves by another 
wire as soon as the button is pushed and B is forced 
down to A. The bottom of the little button rests upon 
the top of B. 

Pig- 53 shows a Table Clamp-Push for use on dining- 
tables, card-tables, chairs, desks, and other movable fur- 





Fig. 54. 



niture. Fig. 54 shows a combination of push-button, 
speaking-tube, and letter-box used in city apartment 
houses. Fig. 55 shows an Indicating Push, The buzzer 
indicates, by the sound, whether the call has been heard; 
that is, the person called answers back. 

Modifications of ordinary push-buttons are used fo: 
floor push-buttons, on doors, windows, etc., for burglar- 
alarms, for turning off or on lights, etc., ^tc. (See 



11 



PUSH-BUTTONS, SWITCHES AND BINDING-POSTS. 45 




Fig. 55. 



'^Apparatus Book, ' ' 

Chapter III., for home- 
made push-buttons.) 
62. Switches have a 

movable bar or plug of 

metal, moving on a pivot, 

to make or break a circuit, 

or transfer a current from 

one condudlor to another. 
Fig. 56 shows a single 

point switch. The cur- 
rent entering the pivoted 

arm can go no farther 

when the switch is open, 

as shown. To close the 

circuit, the arm is pushed 

over until it presses down upon the conta6l-point. For 

neatness, both wires are joined to the under side of the 

switch or to binding-posts. 

Fig. 57 shows a k7iife switch. Copper blades are 

pressed down between copper spring clips to close the 

circuit. The handle is 
made of insulating ma- 
terial. 

Pole - changing 
switches, Fig. 58, are 
used for changing or 
reversing the poles of 
batteries, etc. 

Fig- 59 shows a 
Pig^ 55^ home-made switch, use- 




46 PUSH-BUTTONS, SWITCHES AND BINDING-POSTS. Ill 




Fig. 57- 

current will l)e 
obliged to pass 
through all the 
coils A, B, etc., 
before it can pass 
out at Y. HE 
be moved to 3, 
coils A and B will 
be cut out of the circuit, 
thus decreasing the resist- 
ance to the current on its 
way from X to Y. Cur- 
rent regulators are made 
upon this principle. (See 
'' Apparatus Book," Chap- 
ter IV., for home-made 
switches. ) 

Switchboards are made 
containing from two or 
three to hundreds of 



ful in connedlion with 
resistance coils. By join- 
ing the ends of the coil- 
A, B, C, D, with the 
contadl-points i, 2, 3, 
etc., more or less resist- 
ance can be easily throwni 
in by simply swinging 
the lever E around to 
the left or right. If E 
be turnnd to i, the 




y^ .B c x> 

Fig 59- 



PUSH-BUTTONS, SWITCHES AND BINDING-POSTS. 47 



switches, and are used in telegraph and telephone work, 
in elearic light stations, etc., etc. (See Chapter on 
Central Stations.) Fig. 60 shows a switch used for in- 
candescent lighting 
currents. 

63. Binding- 
Posts are used to 
make connedlions 
between two pieces 
of apparatus, be- 
tween two or more 
wires, between a 
wire and any appa- 
ratus, etc., etc. 
They allow the 
wires to be quickly 
fastened or unfast- 
ened to the apparatus. A large part of the apparatus 
shown in this book has binding-posts attached. Fig. 61 




Fig. 60. 




Fig. 61. 

shows a few of the common forms used. (See ''Appa- 
ratus Book,'' Chapter V., for home-made binding-posts.) 



CHAPTER VI. 

UNITS AND APPARATUS FOR ELECTRICAL. MEASURE- 
MENTS. 

64. Electrical Units. In order to measure elecflricity 
for experimental or commercial purposes, standards or 
units are just as necessary as the inch or foot for measur- 
ing distances. 

65. Potential ; Electromotive Force. If water in 
a tall tank be allowed to squirt from two holes, one near 
the bottom, the other near the top, it is evident that the 
force of the w^ater that comes from the hole at the bottom 
will be the greater. The pressure at the bottom is greater 
than that near the top, because the ' ' head ' ' is greater. 

When a spark of static elecflricity jumps a long distance, 
w^e say that the charge has a high potential ; that is, it 
has a high eledlrical pressure. Potential, for elec?tricity, 
means the same as pressure, for w^ater. The greater the 
potential, or elcfiromotive force (E.M.F.) of a cell, the 
greater its power to push a current through wires. (See 
''Study," § 296 to 305, wdth experiments.) 

66. Unit of E.M.F. ; the Volt.— In speaking of 
water, we say that its pressure is so many pounds to the 
square inch, or that it has a fall, or head, of so man} 
feet. We speak of a current as having so many volts: 
for example, we say that a wdre is carrying a no- volt 
current. The volt is the unit of E.M.F. An ordinary 
gravity cell has an E.M.F. of about one volt. This 
name was given in honor of Volta. 



APPARATUS FOR ELECTRICAL MEASUREMENTS. 49 




67. Measurement of Electromotive Force. There 
are several ways by which the E.M.F. of a cell, for 
example, can be 
measured. It is 
usually measured 
relatively, by com- 
parison with the 
E. M. F. of some 
standard cell . (See 
'^Study," Exp. 
140, for measuring 
the E. M. F. of a 
cell by comparison Fig. 62. 

with the two-fluid cell.) 

Voltmeters are instruments by means of which E.M.F. 
can be read on a printed scale. They are a variety of 
galvanometer, and are made with coils of such high 
resistance, compared with the resistance of a cell or 

dynamo, that the E. AI. F. 
can be read direc5l. The 
reason for this will be seen 
by referring to Ohm's law 
C' Study," §356); the 
resistance is so great that 
the strength of the cur- 
rent depends entirely upon 
the E. M. F. 

Voltmeters measure 
eledlrical pressure just as 
steam gauges measure the pressure of steam. Fig. 62 
shows one form of voltmeter. Fig. 63 shows a voltmeter 




50 APPARATUS FOR KI.ECTRICAIv MEASUREMENTS. 



with illuminated dial. An elec?trical bulb behind the 
instrument furnishes light so that the readings can be 
easily taken. 

68. Electrical Resistance. Did you ever ride down 
hill on a hand-sled ? How easily the sled glides over the 
snow! What happens, though, when you strike a bare 
place, or a place where some evil-minded person ha- 
sprinkled ashes? Does the sled pass easily over bare 

ground or ashes? Snow offers 
very little rcsista7ice to the sled, 
while ashes offer a great resist- 
ance. 

All substances do not allow the 
eledtric current to pass through 
them with the same ease. Even 
the liquid in a cell tends to hold 
the current back and offers in- 
te7'7ial resistance. The various 
wires and instruments connecfted 
to a cell offer external resist- 

ayice, (See '* Study," Chapter XVIII., for experiments, 

etc.) 

69. Unit of Resistance; The Ohm is the name given 
to the unit of resistance. About 9 ft. 9 in. of No. 30 
copper wire, or 39 feet i in. of No. 24 copper wire, will 
make a fairly accurate ohm. 

Resista7ice coils, having carefully measured resistances, 
are made for standards. (See ''Apparatus Book,'* 
Chapter XVII., for home-made resistance coils.) Fig. 
64 shows a commercial form of a standard resistance coil. 
The coil is inclosed in a case and has large wires leading 




Fig. 64. 



APPARATUS FOR KI.KCTRICAI. MEASURE;MKNTS. 5 1 




^ig- ^5. 



from its ends for connedlions. Fig. 65 gives an idea of 
the way in which coils are w^ound and used with plugs to 
build up resistayice boxes, Fig. 66. 

70. Laws of Resistance, i. The resistance of a 
wire is direclly proportional 
to its length, provided its 
cross-sedlion, material, etc., 
are uniform. 

2. The resistance of a wire 
is inversely proportional to its 
area of cross-seclion ; or, in 
other w^ords, inversely propor- 
tional to the square of its 
diameter, other things being 
equal. 

3. The resistance of a ware depends upon its material, 
as well as upon its length, vSize, etc. 

4. The resistance of a wnre increases as its temperature 
rises. (See '\Study," Chapters XVIII. and XIX., for 

experiments on 
resistance, its 
measurement, 
etc.) 

71. Current 
Strength. The 
strength of a cur- 
rent at the end of 
a circuit depends 
not only upon the 
eleSlrical pressure, or E. M. F., w^liich drives the current, 
buf also upon the resistance ^hioh has to be overcome. 




Fig. 66. 



52 APPARATUS FOR ELECTRICAI. MEASUREMENTS. 



The greater the resistance the weaker the current at the 
end of its journe3^ 

72. Unit of Current Strength ; The Ampere. A 
current having an E. M. F. of one volt, pushing its way 
through a rCvSistance of one ohm, would have a unit of 
strength, called one ampere. This current, one ampere 
strong, would deposit, under proper conditions, .0003277 

gramme of copper in 
one second from a sol 11 
tion of copper sulphate 
73. Measurement 
of Current Strength. 
A magnetic needle is 
deflected when a cur- 
rent passes around it, 
as in instruments like 
the galvanometer. The 
gahanoscope merely in- 
dicates the presence of 
a current. Galvajiom- 
eters measure the 
strength of a current, 
and they are made in many forms, depending upon the 
nature and strength of the currents to be measured. 
Galvanometers are standardized, or calibrated, by special 
measurements, or by comparison with some standard in- 
strument, so that w^hen the defledlion is a certain number 
of degrees, the current passing through it is known to 
be of a certain strength. 

Fig. 67 shows an astatic galvanometer. Fig. 68 show 
a ta^igent galvanometer, in which the strength of the cur- 




Fig. 67. 



APPARATUS FOR ELECTRICAL MEASUREMENTS. 53 




Fig. 6S. 



rent is proportional to the tangent of the angle of deflec- 
tion. Fig. 6g shows 2i jD' A rso7iz'a/£'ah'a7io??ieff?', in v^hich 
a coil of wire is suspended between the 
poles of a permanent horseshoe mag- 
net. The lines of force are concen- 
trated by the iron core of the coil. 
The two thin suspending wires conve}' 
the current to the coil. A ray of light 
is reflected from the vSmall mirror and 
acfts as a pointer as in other forms of 
refleAing galvanometers. 

74. The Ammeter, Fig. 70, is a 
form of galvanometer in which the strength of a current, 
in amperes, can be read. In these the strength of current 
is proportional to the angular deflecftions. The coils are 

made with a small resist- 
ance, so that the current 
will not be greatl}' reduced 
in strength in passing 
through them. 

75. Voltameters 
measure the strength of a 
current b}' chemical means, 
the quantity of metal de- 
posited or gas generated 
being proportional to the 
time that the current flows 
and to its strength. In 
the zi'ater voltameter, Fig. 
71, the hydrogen and 
Fig. 69. oxygen produced in a 




54 APPARATUS FOR KI.KCTRICAI. MEASUREMENTS. 




given time are 
measured. (Sec 
''Study," Chapter 
XXI.) 

The copper voltam- 
eter measures the 
amount of copper 
deposited in a given 
time by the current 
Fig. 72 shows one 
form. The copper 
cathode is weighed 

before and after the current flows. The weight of i 

copper deposited and the time taken are used to calculate 

the current strength. 

76. Unit of Quantity; The Coulomb is the quantity^ 

of eledlricity given, in ojie second, by a current having 



Fig. 70. 




Fig. 71. 



APPARATUS FOR ELECTRICAL MEASUREMENTS. 55 




strength of one 
ampere. Time is 
an important ele- 
ment in consider- 
ing the work a cur- 
rent can do. 

77. Electrical 
Horse-power; 
The Watt is the 
unit of eledlrical 
power. A current ^^^' '^^' 

having the strength of one ampere, and an E. M. F. of 
one volt has a unit of power. 746 watts make one elec- 
trical horse-power. Watts = amperes X volts. Fig. 73 
shows a direcft reading wattmeter based on the inter- 
national volt and ampere. They save taking simj^lta- 
neous ammeter and voltmeter readings, which are other- 
wise necessar}^ to 
get the produ6l 
of volts and am- 
peres, and are also 
used on alterna- 
ting current 
measurements. 

There are also 
forms of watt- 
meters. Fig. 74, 
in which the watts 
are read from 
Fig- 73. dials like those on 

an ordinary gas-meter, the records being permanent. 




56 APPARATUS FOR ELECTRICAI. MEASUREMENTS. 



Fig. 75 shows a voltmeter V, and ammeter A, so placed 
in the circuit that readings can be taken. D represents 
a dynamo. A is placed so that the whole current passes 

through it, while V is placed 
between the main wires to 
measure the difference in 
potential. The producfl of the 
two readings in volts and 
amperes gives the number of 
watts. 

78. Chemical Meters also 
measure the quantity of cur- 
rent that is used; for example, 
one may be placed in the cellar 
of current used to lio:ht the 




Fig. 74. 



to measure the quantity 
house. 

Fig. 76 shows a chemical meter, a part of the current 
passing through a jar containing zinc plates and a solu- 
tion of zinc sulphate. Metallic zinc is dissolved from 
one plate and deposited upon the other. The increase in 
weight shows the amount of chemical aclion which is 




Fig. 75. 

proportional to the ampere hours. Knowing the relation 
between the quantit}^ of current that can pass through 
the solution to that which can pass through the meter by 



APPARATUS FOR ELECTRICAL MEASUREMENTS. 57 

another conducftor, a calculation can be made which will 
give the current used. A lamp is so arranged that it 




Fig. 76. 



automatically lights before the meter gets to the freezing- 
point; this warms it up to the proper temperature, at 
which point the light goes out again. 



CHAPTER VII. 

CHEMICAL EFFECTS OF THE ELECTRIC CURRENT. 

79. Electrolysis. It has been seen that in the vol- 
taic cell eledlricity is generated by chemical adlion. Sul- 
phuric acid a(5ls upon zinc and dissolves it in the cell, 
hydrogen is produced, etc. When this process is re- 
versed, that is, when the eleclric current is passed 







Fig. 77. 

through some solutions, they are decomposed, or broken 
up into their constituents. This process is called elenrol- 
ysis, and the compound decomposed is the eleFtrolyte. 
(See '' Study," § 369, etc., with experiments.) 

Fig. 77 shows how water can be decomposed into its 
two constituents, hydrogen and oxygen, there being 
twice as much hydrogen formed as oxygen. 

Fig. 78 shows a glass jar in which are placed two metal 

58 



CHEMICAI. EFFECTS OF THE ELECTRIC CURRENT. 59 



strips, A and C, these being connected with two cells. 
In this jar may be placed various condudling solutions to 
be tested. If, for example, we use a solution of copper 








Fig. 78. 

sulphate, its chemical formula being Cu SO,, the current 
will break it up into Cu (copper) and SO,. The Cu will 
be deposited upon C as the current passes from A to C 
through the solution. A is called the ajiode, and C the 
cathode. 

Fig. 79 shows another form of jar used to study the 
decomposition of solutions by the eleclric - 
current. 

80. Ions. When a solution is decom- 
posed into parts by a current, the parts are 
called the Ions. When copper sulphate 
(CuSOJ is used, the ions are Cu, which is 

I a metal, and SO,, called an acid radical. Y\g 79. 

\ When silver nitrate (Ag NO3) is used, Ag 

and NO3 are the ions. The metal part of the compound 

I goes to the cathode. 



CHAPTER VIII. 

HOW ELECTROPLATING AND ELECTROTYPING ARE DONE. 

8i. Electricity and Chemical Action. We have 
just seen, Chapter VII., that the elecftric current has the 
power to decompose certain compounds when they are in 
solution. By choosing the right solutions, then, we shall 
be able to get copper, silver, and other metals set free by 
ele(?trol3\sis. 

82. Electroplating consists in coating substances 
with metal with the aid of the elecftric current. If we 
wish to ele(5lroplate a piece of metal with copper, for 
example, we can use the arrangement shown in Fig. 78, 
in which C is the cathode plate to be covered, and A is a 
copper plate. The two are in a solution of copper sul- 
phate, and, as^ explained in § 79, the solution will be 
decomposed. Copper will be deposited upon C, and the 
SO4 part of the solution will go to the anode A, which it 
will att^k and gradually dissolve. The SO^, acfting upon 
tli^copper anode, makes Cu SO^ again, and this keeps the 
solution at a uniform strength. The amount of copper 
dissolved from the copper anode equals, nearly, the 
amount deposited upon the cathode. The metal is carried 
in the direction of the current. 

If we wish to plate something with silver or gold, it 
will be necessary to use a solution of silver or gold for 
the eledlrolyte, a plate of metallic silver or gold being 
used for the anode, as the case may be. 

60 



KI.KCTROPI.ATING AND KLKCTROTYPING. 



6l 



Great care is used in cleaning substances to be plated, 
all dirt and grease being carefully removed. 

Fig. 80 vShows a plating bath in which several articles 
can be plated at the same time by hanging them upon a 
metal bar which really forms a part of the cathode. If, 
for example, we wish to plate knives, spoons, etc., with 
silver, they would be hung from the bar shown, each 
being a part of the cathode. The vat would contain a 
solution of silver, and from the other bar would be hung 




Fig. 80. 



a silver plate having a surface about equal to that of the 
combined knives, etc. 

Most metals are coated with copper before the}^ are 
plated with silver or gold. When plating is done on a 
large scale, a current from a dynamo is used. For 
experimental purposes a Gravity cell will do very well. 
(See *' Study," .§ 374 to 380 with experiments.) 

83. Electrotyping. It was observed b}^ De La Rue 
in 1836 that in the Daniell cell an even coating of copper 
was deposited upon the copper plate. From this was 
developed the process of eledlrotyping, which consists in 



62 KlvKCTROPIvATlNG AND ELKCTROTYPING. 

making a copy in metal of a wood-cut, page of type, etc. 
A mould or impression of the type or coin is first 
made in wax, or other suitable material. These moulds 
are, of course, the reverse of the original, and as they do 
not condudl eledlricity, have to be coated with graphite. 
This thin coating lines the mould with conducting 
material so that the current can get to every part of the 
mould. These are then hung upon the cathode in a bath 
of copper sulphate as described in §82. The elecftric 
current which passes through the vat deposits a thin 
layer of metallic copper next to the graphite. When this 
copper gets thick enough, the wax is melted away from 
it, leaving a thin shell of copper, the side next to the 
graphite being exacftly alike in shape to the type, but 
made of copper. These thin copper sheets are too thin 
to stand the pressure necessary on printing presses, so 
the}^ are strengthened b}- backing them with soft metal 
which fills every crevice, making solid plates about % in. 
thick. These plates or elcH retypes are used to print 
from, the original type being used to set up another page. 



CHAPTER IX. 



THE STORAGE BATTERY, AND HOW IT WORKS. 



84. Polarization. It has been stated that a simple 
cell polarizes rapidly on account of hydrogen bubbles that 
form upon the copper plate. They tend to send a current 
in the opposite direction to that of the main current, 
which is thereby weakened. 

85. Electromotive Force of Polarization. It has 
been shown. Fig. 71, that water can be decomposed by 

the eleclric current. 
Hydrogen and 
oxygen have a 
strong attraction or 
chemical affinity for 
each other, or the}^ 
would not unite to 
form water. This 
attradlion has to be 
overcome before the 
water can be decomposed. As soon as the decomposing 
current ceases to flow, the gases formed try to rush to- 
gether again; in fact, if the water voltameter be discon- 
nedled from the cells and connedted with a galvanoscope, 
the presence of a current will be shown. This voltam- 
eter will give a current w4th an E. M. F. of nearly 1.5 
volts; so it is evident that w^e must have a current w^th a 
higher voltage than this to decompose water. This 

63 




Fig. Si. 



64 'I'HE STORAGE BATTERY, AND HOW IT WORKS. 



E. M. F., due to polarization, is called the E. M. F. of 
polarization. 

86. Secondary or Storage Batteries, also called 
accitmidators , do not reall}^ store electricity. They must 
be charged by a current before they can give out any 
elecftricity. Chemical changes are produced in the stor- 
age cells by the charging current just as they are in vol- 
tameters, elecftroplating solutions, etc. ; so it is potential 

chemical energy that is really 
stored. When the new prod- 
uces are allowed to go back 
to their original state, by 
joining the elecflrodes of the 
charged cell, a current is pro- 
duced. 

Fig. 8 1 shows two lead 
plates, A and B, immersed in 
dilute sulphuric acid, and 
conne(5led with two ordinary 
cells. A strong current will 
pass through the liquid be- 
tween A and B at first, but it 
will quickly become weaker, as chemical changes take 
place in the liquid. This may be shown by a galva- 
nometer put in the circuit before beginning the experi- 
ment. By disconnedting the wires from the cells and 
joining them to the galvanometer, it will be shown that 
a current comes from the lead plates. This arrangement 
may be called a simple storage cell. Regular storage cells 
are charged with the current from a dynamo. (See 
''Study," Exp. 151.) 




THE STORAGE BATTERY, AND HOW IT WORKS. 65 

The first storage cells were made of plain lead plates, 
rolled up in such a way that ' they were close to each 
other, but did not touch. These were placed in dilute 
sulphuric acid. They were charged in alternate direc- 
tions several times, until the lead became properly acted 
upon, at which time the cell would furnish a current. 

A great improvement was made in 1881, by Faure, who 
coated the plates with red lead. 

The method now generally practiced is to cast a frame 




Fig. S3. 

of lead, with raised right-angled ribs on each side, thus 
forming little depressed squares, or to punch a lead plate 
full of holes, which squares or holes are then filled with 
a pasty mixture of red oxide of lead in positive plates, 
and with litharge in negatives. In a form called the 
chloride battery, instead of cementing lead oxide paste 
into or against a lead framing in order to obtain the 
necessary a(flive material, the latter is obtained by a 
stridlly chemical process. 



66 THE STORAGE BATTERY, AND HOW IT WORKS. 

Fig. 82 shows a storage cell with plates, etc., containe 
in glass jar. Fig. 83 shows a cell of 41 plates, set up ir 
a lead-lined wood tank. Fig. 84 shows three cells joined 
in series. Many storage cells are used in central electric 
light stations to help the dynamos during the ' ' rush ' ' 
hours at night. They are charged during the day when 
the load on the dynamos is not heavy. 

Fig. 85 shows another form of storage cell containing 
a number of plates. 

87. The Uses of Storage Batteries are almost 



'"^^^^mm 




Fig. 84. 



numberless. The current can be used for nearly every- 
thing for which a constant current is adapted, the follow- 
ing being some of its applications: Carriage propulsion; 
eledlric launch propulsion; train lighting; yacht lighting; 
carriage lighting; bicycle lighting; miners' lamps; den- 
tal, medical, surgical, and laboratory work; phonographs: 
kinetoscopes; automaton pianos; sewing-machine motors 
fan motors; telegraph; telephone; ele(5lric bell; eledlric 



THK vSTORAGE BATTERY, AND HOW IT WORKS. 67 

fire-alarm; heat regulating; railroad switch and signal 
apparatus. 

By the installing of a storage plant many natural but 
small sources of power may be utilized in furnishing light 
and power; sources which otherwise are not available, 
because not large enough to supply maximum demands. 
The force of the tides, of small water powers from irri- 
gating ditches, and even of the wind, come under this 
heading. 

As a regulator of pressure, in case of fluctuations in 




Fig. 85. 

the load, the value of a storage plant is inestimable. 
These fludluations of load are particularly noticeable in 
eledlric railway plants, where the demand is constantly 
rising and falling, sometimes jumping from almost noth- 
ing to the maximum, and vice versa, in a few seconds. 
If for no other reason than the prevention of severe 
strain on the engines and generators, caused by these 
fludluations of demand, a storage plant will be valuable. 



CHAPTER X. 

HOW ELECTRICITY IS GENERATED BY HEAT. 

88. Thermoelectricity is the name given to ele(5lricity 
that is generated by heat. If a strip of iron, I, be con- 
nedled between two strips of copper, C C, these being 
joined by a copper wire, C W, we shall have an arrange- 
ment that wall generate a current when heated at either 
of the jundtions betw^een C and I. When it is heated 

at A the current will 
flow as shown b\' 
arrows, from C to I. 
If we heat at B, the 
current will flow in 
the opposite direction 
through the metals, 
although it will still 
go from C to I as before. Such currents are called 
thermoele^lyic currents. 

Different pairs of metals produce different results. 
Antimony and bismuth are generally used, because the 
greatest eflfedl is produced by them. If the end of a strip 
of bismuth be soldered to the end of a similar strip of 
antimony, and the free ends be connedled to a galvanom- 
eter of low resistance, the presence of a current will be 
shown when the point of contac5l becomes hotter than the 
rest of the circuit. The current will flow from bismuth 

68 




Fig. 86. 



HOW ELECTRICITY IS GENERATED BY HEAT. 



69 



to antimony across the joint. By cooling the jundlure 
below the temperature of the rest of the circuit, a current 
will be produced in the opposite direction to the above. 
The energy of the current is kept up by the heat absorbed, 
just as it is kept up by chemical action in the voltaic 
cell. 

89. Peltier Effect. If an elec5lric current be passed 
through pairs of metals, the parts at the junction become 
slightly warmer or cooler than before, depending upon 
the diredlion of the current. This aclion is really the 
reverse of that in which currents are produced by heat. 

90. Thermopiles. As the E.M.F. of the current 
produced by a vsingle pair of metals is very small, vSeveral 




Fig. 87. 



pairs are usually joined in series, so that the different 
currents will help each other by flowing in the same direc- 
tion. Such combinations are called thermoelec5lric piles, 
or simply thermopiles. 

Fig 87 shows such an arrangement, in which a large 
number of elements are placed in a small space. The 
jundlures are so arranged that the alternate ones come 
together at one side. 

Fig. 88 show^s a thermopile connec?ted with a galvanom- 



70 HOW KI.KCTRICITY IS GENERATED BY HEAT. 



eter. The heat of a match, or the cold of a piece of ice, 
will produce a current, even if held at some distance from 




m 




Fig. 88. 



the thermopile. The galvanometer should be a short- 
coil astatic one. (See ''Study,'* Chapter XXIV., for 
experiments and home-made thermopile.) 



CHAPTER XI. 



MAGNETIC EFFECTS OF THE ELECTRIC CTJRRENT. 

91. Electromagnetism is the name given to magnet- 
ism that is developed by eledlricity. We have seen that 
if a magnetic needle be placed in the field of a magnet, its 
N pole will point in the dire(5lion taken by the lines of 
force as they pass from the N to the S pole of the magnet. 

92. Lines of Force about a Wire. When a current 




Fig. 89. 

passes through a wire, the magnetic needle placed over or 
under it tends to take a position at right angles to the 
wire. Fig. 89 shows such a wire and needle, and how 
the needle is defledled; it twists right around from its N 
and S position as soon as the current begins to flow. 
This shows that the lines of force pass around the wire 
and not in the diredlion of its length. The needle does 
not swing entirely perpendicular to the wire, that is, to 

71 



72 MAGNETIC KFI^ECTS OF KI.KCTRIC CURRENT. 

the E and W line, because the earth is at the same time 
pulling its N pole toward the N. 

Fig. 90 shows a bent wire through which a current 
passes from C to Z. If you look along the wire from C 
toward the points A and B, you will see that tmder the 
wire the lines of force pass to the left. Looking along 
the wire from Z toward D you will see that the lines of 
force pass opposite to the above, as the current comes 
toward you. This is learned by experiment. (See 
^' Study," Exp. 152, §385, etc.) 

Rule, Hold the right hand with the thumb extended 
(Fig. 89) and with the fingers pointing in the diredlion of 





Fig. 91. 

the current, the palm being toward the needle and on 
the opposite side of the wire from the needle. The north- 
seeking pole will then be deflecfted in the diredlion in 
which the thumb points. 

93. Current Detectors. As there is a magnetic field 
about a wire when a current passes through it, and as the 
magnetic needle is affedled, we have a means of detedling 
the presence of a current. When the current is strong it 
is simply necessary to let it pass once over or under a 
needle; when it is weak, the wire must pass several 
times above and below the needle, Fig. 91, to give the 
needlemotion. (See ''Apparatus Book," Chapter XIII., 
for home-made detedlors. ) 



MAGNETIC EFFECTS OF ELECTRIC CURRENT. 



73 




Fig. 92. 



94. Astatic Needles and Detectors. By arranging 
two magnetized needles with their poles opposite each 
other, Fig. 92, an astatic needle is formed. The point- 
ing-power is almost nothing, although their magnetic 
fields are retained. This com- 
bination is used to detect feeble 
currents. In the ordinary de- 
tedlor, the tendency of the needle 
to point to the N and S has to be 
overcome by the magnetic field 
about the coil before the needle 

can be moved; but in the astatic detector and galvano- 
scope this pointing-power 'is done away with. Fig. 93 
shows a simple astatic galvanoscope. Fig. 67 shows an 
astatic galvanometer for measuring weak currents. 

95. Polarity of Coils. When a current of eledlricity 
passes through a coil of wire, the 
coil adls very much like a magnet, 
although no iron enters into its 
constru(ftion. The coil becomes 
magnetized by the elecT:ric cur- 
rent, lines of force pass from it 
into the air, etc. Fig. 94 shows a 
coil connec5ted to copper and zinc 
plates, so arranged with cork that 
the whole can float in a dish of 
dilute sulphuric acid. The cur- 

rent passes as shown by the 
arrows, and when the N pole of a magnet is brought 
near the right-hand end, there is a repulsion, showing 
that that end of the coil has a N pole. 




74 



MAGNETIC EFFECTS OF ELECTRIC CURRENT. 



Rule. When you face the right-hand end of the coil, 
the current is seen to pass around it in an an ti -clockwise 
diredlion; this produces a N pole. When the current 1| 
passes in a clockwise direction a S pole is produced. 

96. Electromagnets. 
A coil of wire has a stronger 
field than a straight wire 
carrying the same current, 
because each turn adds its 
field to the fields of the 
other turns. By having the 
central part of the coil 
made of iron, or by having 
the coil of insulated wire 
wound upon an iron core, /•^ 
the strength of the mag- 
netic field of the coil is 
greatly increased. 

Lines of force do not 
pass as readily through air 
as through iron ; in fact, 

lines of force will go out of their way to go through 
iron. With a coil of wire the lines of force pass from its 
N pole through the air on all sides of the coil to its S 
pole; they then pass through the inside of the coil and 
through the air back to the N pole. When the resist- 
ance to their passage through the coil is decreased by the 
core, the magnetic field is greatl}- strengthened, and we 
have an eletlro77iag7iet. 

The coil of wire temporarily magnetizes the iron core; 
it can permanently magnetize a piece of steel used as 




Fig. 94. 



MAGNETIC EFFECTS OF EI.ECTRIC CURRENT. 75 
'Study," Chapter XXII., for experi- 



(See 



a core, 
ments. ) 

97. Forms of Electromagnets. Fig. 95 shows a 
straight, or bar electromagnet. Fig. 96 shows a simple 
form of horseshoe eleBromagnet. As this form is not easily 
wound, the coils are generally wound on two separate 




Fig. 95- 

cores which are then joined by a yoke. The yoke 
merely takes the place of the cur\' ed part shown in Fig. 
96. In Fig. 97 is shown the ordinary form of horseshoe 
eledlromagnet used for all sorts of eledlrical instruments. 
(See '' Apparatus Book," Chapter IX., for home-made 
electromagnets. ) 

98. Yokes and Armatures. In the horseshoe magnet 
there are two .poles to attracft and two to induce. The 
lines of force pass through the 3^oke on their way from 
one core to the other, instead of going through the air. 



76 



MAGNETIC EFFECTS OF ELECTRIC CURRENT. 



This reduces the resistance to them. If we had no yokd 
we should simply have two straight eledlromagnets, an<j 
the resistance to the lines of force would be so great tha 





Fig. 96. 



Fig. 97. 



the total strength would be nuich reduced. Yokes are 
made of soft iron, as well as the cores and armature. The 
armahire, as with permanent horseshoe magnets, is 
strongly drawn toward the poles. As soon as the cur- 
rent ceases to flow, the attracflion also ceases. 

Beautiful magnetic figures can be made with horseshoe 




(D 



Fig. 9S. 



magnets. Fig. 98 shows that the coils must be joined so 
that the current can pass around the cores in opposite 
diredlions to make unlike poles. (See '\Study," Exp. 
164 to 173.) 



CHAPTER XII. 

HOW ELECTRICITY IS GENERATED BY INDUCTION. 

99. Electromagnetic Induction. We have seen that 
a magnet has the power to act through space and induce 
another piece of iron or steel to become a magnet. A 
charge of static elecftricity can induce a charge upon 
another condudlor. We have now to see how a current 
of elecftricity in one conduAor can induce a current in 





Fig. 99. 



Fig. 100. 



another condu(5tor, not in any wa}^ connecfted with the 
first, and how a magnet and a coil can generate a current. 
100. Current from Magnet and Coil. If a bar mag- 
net, Fig. 99, be suddenh' thrust into a hollow^ coil of 
wire, a momentary current of electricity wall be generated 
in the coil. No current passes w^hen the magnet and coil 
are still; at least one of them must be in motion. Such a 
current is said to be ijidiiced, and is an inverse one when 



77 



78 



ELECTRICITY GENERATED BY INDUCTION. 



the magnet is inserted, and a direR one when the magnet 
is withdrawn from the coil. 

loi. Induced Currents and Lines of Force. Per- 
manent magnets are constantly sending out thousands of 
lines of force. Fig. loo shows a bar magnet entering a 
coil of wire; the number of lines of force is increasing, 
and the induced current passes in an anti-clockwise direc- 
tion when looking down into the coil along the lines of 




Fig. loi. 



force. This produces an indirect current. If an iron 
core be used in the coil, the induced current will be 
greatly strengthened. 

It takes force to move a magnet through the center of 
a coil, and it is this work that is the source of the induced 
current. We have, in this simple experiment, the key to 
the adlion of the dynamo and other elecftrical machines. « 

102. Current from two Coils. Fig. loi shows twc I 
coils of wire, the smaller being connecfted to a cell, the 
larger to a galvanometer. By moving the small coil up 

111 



ELECTRICITY GENERATED BY INDUCTION. 79 

and down inside of the large one, induced currents are 
generated, first in one diredlion and then in the opposite. 
We have here two entirely separate circuits, in no way 
connecfled. The primary current comes from the cell, 
while the secondary current is an induced one. By placing 
a core in the small coil of Fig. loi, the induced current 
will be greatly strengthened. 

It is not necessary to have the two coils so that one or 
both of them can move. They may be wound on the 
same core, or otherwise arranged as in the induction coil. 
(See ''Study," Chapter XXV., for experiments on 
induced currents.) 



CHAPTER XIII. 

HOW THE INDUCTION COIL WORKS. 

103. The Coils. We saw, § 102, that an induced 
current was generated when a current-carrying coil, Fig. 
loi, was thrust into another coil connecfled with a galva- 
nometer. The galvanometer was used merely to show the 
presence of the current. The primary coil is the one 
connedled wdth the cell; the other one is called \^^ second- 
ary coil. 

When a current suddenly begins to flow through a coil, 




Fig. 102. 

the effedl upon a neighboring coil is the same as that pro- 
duced by suddenly bringing a magnet near it; and when 
the current stops, the opposite effedl is produced. It is 
evident, then, that w^e can keep the small coil of Fig. loi 
with its core inside of the large coil, and generate induced 
currents by merely making and breaking the primary 
circuit. 



HOW THE INDUCTION COIL WORKS. 8 1 

We may consider that when the primar>^ circuit is 
closed, the lines of force shoot out through the turns of 
the secondary coil j ust as they do when a magnet or a 
current-carrying coil is thrust into it. Upon opening the 
circuit, the lines of force cease to exist; that is, we may 
imagine them drawn in again. 

104. Construction. Fig. 102 shows one form of 
home-made indudlion coil, given here merely to explain 
the adlion and connecT:ions. Nearly all indudtion coils 
have some form of automatic current interrupter, placed 
in the primary circuit, to rapidly turn the current off 
and on. 

Details of Figs. 102 and 103. Wires 5 and 6 are the 
ends of the primary coil, while 
wires 7 and 8 are the terminals of 
the secondary coil. The primary 
coil is wound on a bolt which 
serv^es as the core, and on this 
coil is wound the secondary which p- ^^^ 

consists of many turns of fine wire. 

The wires from a battery should be joined to binding- 
posts W and X, and the handles, from which the shock is 
felt, to Y and Z. Fig. 103 shows the details of the in- 
terrupter. 

If the current from a cell enters at W, it will pass 
through the primary coil and out at X, after going 
through 5, R, F, S I, B, E and C. The instant the 
current passes, the bolt becomes magnetized; this attradls 
A, which pulls B away from the end of SI, thus auto- 
matically opening the circuit. B at once springs back to 
its former position against S I, as A is no longer attracfted; 




82' HOW THK INDUCTION COIL WORKS. 

the circuit being closed, the operation is rapidly 
repeated. 

A co7idenser is usually connedled to commercial forms. 
It is placed under the wood- work and decreases sparking 
at the interrupter. (See '* Apparatus Book," Chapter 
XI., for home-made indudlion coils.) 

Fig. 104 shows one form of coil. The battery wires 
are joined to the binding-posts at the left. The secondary 
coil ends in two rods, and the spark jumps from one to 




Fig. 104. 

the other. The interrupter and a switch are shown at 
the left. 

Fig. 105 shows a small coil for medical purposes. A 
dry cell is placed under the coil and all is included in 
a neat box. The handles form the terminals of the 
secondary coil. | 

105. The Currents. It should be noted that the 
current from the cell does not get into the secondary coil.( 
The coils are thoroughly insulated from each other. The 
secondary current is an induced one, its voltage depending 
upon the relative number of turns of wire there ar 



HOW THE IXDUCTIOX COIIv WORKS. 83 

in the two coils. (See Transformers.) The secondary 
current is an alternating one; that is, it flows in one 
direction for an instant and then immediately reverses its 
diredlion. The rapidity of the alternations depends upon 
the speed of the interrupter. Coils are made that give a 
secondary current with an enormous voltage; so high, in 
facft, that the spark will pass many inches, and otherwise 
adl like those produced by static eledlric machines. 




Fig. 105. 



106. Uses of Induction Coils. Gas-jets can be 
lighted at a distance with the spark from a coil, by ex- 
tending wires from the secondar}^ coil to the jet. Powder 
can be fired at a distance, and other things performed, 
when a high voltage current is needed. Its use in medi- 
cine has been noted. It is largely used in telephone work. 
i Of late, great use has been made of the secondary current 
i in experiments with vacuum-tubes, X-ray work, etc. 



CHAPTER XIV. 



THE ELECTRIC TELEGRAPH, AND HOW IT SENDS 
MESSAGES. 



107. The Complete Telegraph Line consists of 
several instruments, switches, etc., etc., but its essential 
parts are: The Line, or wire, w^hich connec5ls the diflFer- 
ent stations; the Transmitter or Key; the Receiver 01 
So2inder, and the Battery or Dynamo. 

108. The Line is made of strong copper, iron, or soft 
steel ware. To keep the current in the line it is insu- 
lated, generally upon poles, by glass insulators. For 

very short lines tw^o wires 
can be used, the line wire 
and the return; but for long 
lines the earth is used as a 
return, a wire from each 
end being joined to large metal plates sunk in the earth. 

109. Telegraph Keys are merely instruments by 
which the circuit can be conveniently and rapidly opened 
or closed at the wall of the operator. An ordinary push- 
button may be used to turn the current off and on, but it 
is not so convenient as a key. 

Fig. 106 shows a side view of a simple key which cm 
be put anywhere in the circuit, one end of the cut wire 
being attached to X and the other to Y. By moving the 
lever C up and down according to a previously arranged 
set of signals, a current will be allowed to pass to a dis- 

8i 




Fig. 106. 



THE ELECTRIC TEI.EGRAPH. 



85 



tant station. As X and Y are insulated from each other, 
the current can pass only when C presses against Y. 
Fig. 107 shows a regular key, with switch, which is 




Fig. 107. 

used to allow the current to pass through the instrument 
when receiving a message. 

110. Telegraph Sounders receive the current from 
some distant station, and with its elecftromagnet produce 
sounds that can be translated into messages. 

Fig. 108 shows simply an eledlromagnet H, the coil 
being connedled in series with a ke}' K and a cell D C. 
The key and D C are shown by a top view. The lever 
of K does not touch the other metal strap until it is 
pressed down. A little above the core of H is held a 
strip of iron, or armature I. As soon as the circuit is 




Fig. 108. 



closed at K, the current rushes through the circuit, and 
the core attracts I making a distindl click. As soon as 
K is raised, I springs awa}^ from the core, if it has been 



86 



THE KI.KCTRIC TELEGRAPH. 



properly held. In regular instruments a click is also 
made when the armature springs back again. 

The time between the two clicks can be short or long, 

to represent dots or dashes, 
which, together with spaces, 
represent letters. ( For 
Telegraph Alphabet and 
complete direcftions for 
home-made keys, sounders, 
etc., see ''Apparatus 
I^ook,'' Chapter XIV.) 

Fig. 109 shows a form of 

home-made sounder. Fig. 

1 10 shows one form of telegraph sounder. Over the poles 

of the horseshoe eledlromagnet is an armature fixed to a 

metal bar that can rock up and down. The instant the 








current passes through the coils the armature comes 
down until a stop-screw strikes firmly upon the metal 
frame, making the down click. As soon as the distant 



THE ELECTRIC TELEGRAPH. 



87 



key is raised, the armature is firmly pulled back and 
another click is made. The two clicks differ in sound, 
and can be readily recognized by the operator. 

111. Connections for Simple Line. Fig. m shows 
complete connedlions for a home-made telegraph line. 
The capital letters are used for the right side, R, and 
small letters for the left side, L. Gravity cells, B and b, 
are used. The souiiders, S and s, and the keys, K and k, 
are shown by a top view. The broad black lines of S and 
s represent the armatures which are direcftly over the 
eledlromagnets. The keys have switches, E and e. 

The two stations, R and L, may be in the same room, 
or in different houses. 
The return wire, R W, 
passes from the copper 
of b to the zinc of B. 
This is important, as the 
cells must help each 
other; that is, they are 
in series. The line wire, 
ly W, passes from one 

station to the other, and the return may be through the 
wire, R W, or through the earth; but for short lines a 
wire is best. 

112. Operation of Simple Line. Suppose two boys, 
R (right) and I, (left) have a line. Fig. 11 1 shows that 
R's switch, E, is open, while e is closed. The entire 
circuit, then, is broken at but one point. As soon as R 
presses his key, the circuit is closed, and the current from 
both cells rushes around from B, through K, S, Iv W, s, 
k, b, R W, and back to B. This makes the armatures of 




88 



THK KI.ECTRIC TELEGRAPH. 



S and s come down with a click at the same time. As 
soon as the key is raised, the armatures lift and make 
the up-click. As soon as R has finished, he closes his 
switch E. As the armatures are then held down, L 
knows that R has finished, so he opens his switch e, and 
answers R. Both E and e are closed when the line is not 
in use, so that either can open his switch at any time and 
call up the other. Closed circuit cells must be used for 
such lilies. On very large lines dynamos are used to 
furnish the current. 

113. The Relay. Owing to the large resistance of 
long telegraph lines, the current is weak when it reaches 
a distant station, and not strong enough to work an 




F i tr • 



ordinary vsounder. To get around this, relays are used; 
these are very delicate instruments that replace the 
sounder in the line wire circuit. Their coils are usually 
wound with many turns of fine wire, so that a feeble 
current will move its nicely adjusted armature. The 
relay armature merely adls as an automatic key to open 
and close a local circuit which includes a battery and 
sounder. The line current does not enter the sounder; it 
passes back from the relay to the sending station through 
the earth. 

Fig. 112 gives an idea of simple relay connedlions. 
The key K, and cell D C, represent a distant sending 
station. E is the eledlromagnet of the relay, and R A is 



II 



THK KI.ECTRIC TEI.KGRAPH. 89 

its armature. L W and R W represent the line and 
return wires. R A will vibrate toward E every time K 
is pressed, and close the local circuit, w^hich includes a 
local battery, L B, and a sounder. It is evident that as 
soon as K is pressed the sounder wall w^ork with a good 
strong click, as the local battery can be made as strong 
as desired. 

Fig. 113 shows a regular instrument which opens and 
closes the local circuit at the top of the armature. 

114. Ink Writing Registers are frequently used 




Fig. 113. 

instead of sounders. Fig. 114 shows a writing register 
that starts itself promptly at the opening of the circuit, 
and stops automatically as soon as the circuit returns to 
its normal condition. A strip of narrow paper is slowly 
pulled from the reel by the machine, a mark being made 
upon it every time the armature of an inclosed eledlro- 
magnet is attracted. When the circuit is simply closed 
for an. instant, a short line, representing a dot, is made. 

Registers are built both single pen and double pen. 
In the latter case, as the record of one wire is made with 



90 THK KI.ECTRIC TELEGRAPH. 

a fine pen, and the other with a coarse pen, they can 
always be identified. The record being blocked out upon 
white tape in solid black color, in a series of clean-cut 




Fig. 114. 

dots and dashes, it can be read at a glance, and as it is 
indelible, it may be read years afterward. Registers are 
made for local circuits, for use in connedlion with relays, 
or for diredl use on main lines, as is usually desirable in 
fire-alarm circuits. 



CHAPTER XV. 



THE ELECTRIC BELL AND SOME OF ITS USES. 

115. Automatic Current Interrupters are used on 
most common bells, as well as on induction coils, etc. 
(See§ 104.) Fig. 115 
shows a simple form 
of interrupter. The 
wire I, from a cell D 
C, is joined to an iron 
strip I a short distance 
from its end. The 




Fig. 115. 



other wire from D C passes to one end of the eledlro- 
magnet coil H. The remaining end of H is placed in 
contadl with I as shown, completing the circuit. As soon 
as the current passes, I is pulled down and away from 
the upper wire 2, breaking the circuit. I, being held b}^ 
its left-hand end firmly in the hand, immediately springs 
back to its former position, closing the circuit again. 




This adlion is repeated, the rapidity of the vibrations 
depending somewhat upon the position of the wires on I. 
In regular instruments a platinum point is used where 

91 



92 THK KI.KCTRIC BEI.I. AND SOME OF ITS USES. 




fore pressing K 
vibrate rapidly, 
the vibrating armature, so 
that it will be struck by I at 
each vibration, we should 
have a simple eledlric bell. 
This form of elec5lric bell is 
called a trembling bell, on 
account of its vibrating ar- 
mature. 

Fig. 117 shows a form of 
trembling bell wdth cover 
removed. Fig. 118 shows a 
single- stroke bell, used for 
fire-alarms and other signal work 



the circuit is broken ; this stands 
the sparking w^hen the armature 
vibrates. 

116. Electric Bells may be 
illustrated by referring to Fig. 
116, w^hich shows a circuit sim- 
ilar to that described in § 115, 
but which also contains a key 
K, in the circuit. This allows 
the circuit to be opened and 
closed at a distance from the 
vibrating armature. The cir- 
cuit must not be broken at two 
places at the same time, so wires 
should touch at the end of I be- 
Upon pressing K the armature I w^U 
By placing a small h^W near the end of 




Fig. 118. 
In this the armature ' 



is attracfted but once each time the current passes. As 



\ 



I 



THE ELECTRIC BELL AND SOME OF ITS USES. 93 




Fig. 119. 



many taps of the bell can be 

given as desired by pressing 

the push-button. Fig. 119 

shows a gong for railway 

crossings, signals, etc. Fig. 

120 shows a circuit including 

cell, push-button, and bell, 

with extra wire for lengthen- 
ing the line. 
Electro- Mechanical Gongs are 

used to give loud signals for 

special purposes. The me- 
chanical device is started by 

the eledlric current w^hen the 

armature of the eledlromagnet 

is attradled. Springs, weights, etc., are used as 
121 shows a small bell of this kind. 

117. Magneto Testing Bells, 
Fig. 122, are really small hand- 
power d3^namos. The armature is 
made to revolve between the poles 
of strong permanent magnets, and 
it is so wound that it gives a cur- 
rent with a large E. M. F., so that 
it can ring through the large re- 
sistance of a long line to test it. 

Magneto Signal Bells, Fig. 123, 
are used as generator and bell in 
connexion with telephones. The 
generator, used to ring a bell at a 

distant station, stands at the bottom of the box. The 



the 



power. Fi^ 




Fig. 120. 



94 I'HK EI.ECTRIC BELIy AND SOME OF ITS USES. 



bell is fastened to the lid, and receives current from a 
distant bell. 

Ii8. Electric Buzzers have the same general con- 
strudlion as eledlric bells; in fadl, you will have a buzzer 





Fig. 121. 




Fig. 122. 




Fig. 124. 

by removing the bell from an ordinary eledlric bell. 
Buzzers are used in places where the loud sound of a bell 
would be objedlionable. Fig. 124 shows the usual form 
of buzzers, the cover being removed. 



CHAPTER XVI. 

THE TELEPHONE, AND HOW IT TRANSMITS SPEECH. 

119. The Telephone is an instrument for reproduc- 
ing sounds at a distance, and electricity is the agent by 
which this is generally accomplished. The part spoken 
to is called the transmitter, and the part which gives 





Fig. 125. 



Fig. 126. 



sound out again is called the receiver, Sound itself does 
not pass over the line. While the same apparatus can be 
used for both transmitter and receiver, they are generally 
different in construdtion to get the best results. 




Fig. 127. 

120. The Bell or Magneto-transmitter generates 
its own current, and is, stridlly speaking, a dynamo that 

95 



96 



HOW THE TELEPHONK TRANSMITS SPEECH. 



is run by the voice. It depends upon inducftion for its 
adlion. 

Fig. 125 shows a coil of wire, H, with soft iron core, 
the ends of the wires being connecfled to a dehcate gal- 
vanoscope. If one pole of the magnet H M be suddenly 




Fig. 128. 



moved up and down near the core, an alternating current 
will be generated in the coil, the circuit being completed 
through the galvanoscope. As H M approaches the core 
the current will flow in one direcftion, and as H M is 
withdrawn it will pass in the opposite direcftion. The 
combination makes a miniature alternating dynamo. 

If we imagine the soft iron core of H, Fig. 125, taken 
out, and one pole of HM, or preferably that of a bar 
magnet stuck through the coil, a feeble current will also 
be produced by moving the soft iron 
back and forth near the magnet's pole. 
This is really what is done in the 
Bell transmitter, soft iron in the shape 
of a thin disc (D, Fig. 126) being 
made to vibrate by the voice immedi- 
ately in front of a coil having a per- 
manent magnet for a core. The disc, 
or diaphragm , as it is called, is fixed 
near, but it does not touch, the magnet. It is under a 
constant strain, being attracted by the magnet, so it^ 




Fig. 129. 



HOW THE TELEPHONE TRANSMITS SPEECH. 



97 



slightest movement changes the strength of the magnetic 
field, causing more or less lines of force to shoot through 
the turns of the coil and induce a current. The coil con- 



\¥^ 



r^ 



Ql 



Fig. 130. 

sists of many turns of fine, insulated wire. The current 
generated is an alternating one, and although exceedingly 
small can force its way through a long length of wire. 

Fig. 127 shows a section of a regular transmitter, and 
Fig. 128 a form of compound magnet frequently used in 
the transmitter. 
Fig. 129 shows 
a transmitter 
with cords which 
contain flexible 
wires. 

121. The Re- 
ceiver, for short 
lines, may have 
the same con- 
strucftion as the 
Bell transmitter. 
Fig. 130 shows 
a diagram of two 
Bell receivers, either being used as the transmitter and 
the other as the receiver. As the alternating current 
goes to the distant receiver, it flies through the coil 
first in one diredion and then in the other. This al- 




Fig. 131. 



98 HOW THK TELEPHONE TRANSMITS SPEECH. 

ternately strengthens and weakens the magnetic field 
near the diaphragm, causing it to vibrate back and forth 
as the magnet pulls more or less. The receiver dia- 
phragm repeats the vibrations in the transmitter. 




y®^ 



jx: /v\c 




Fig. 132. 

Nothing but the induced ele<5lric current passes over the 
wires. 

122. The Microphone. If a current of eledlricity be 
allowed to pass through a circuit like that shown in Fig. 
131, which includes a battery, a Bell receiver, and a 
microphone, any vslight sound near the microphone will 
be greatly magnified in the receiver. The microphone 
consists of pieces of carbon so fixed that they form loose 
contacts. Any slight movement of the carbon causes the 
resistance to the current to be greatly changed. The 
rapidly varying resistance allows more or less current to 
pass, the result being that this pulsating current causes 
the diaphragm to vibrate. The diaphragm has a con- 
stantly varying pull upon it when the carbons are in any 




X. 



Fig. 133- 

way disturbed by the voice, or by the ticking of a watch, 

etc. This principle has been made use of in carbon 

transmitters, which are made in a large variety of forms. 

123. The Carbon Transmitter does not, in itself, 



HOW THE TELEPHONE TRANSMITS SPEECH. 



99 



generate a current like the magneto-transmitter; it merely 
produces changes in the strength of a current that flows 
through it and that comes from 
some outside source. In Fig. 
132, X and Y are two carbon 
buttons, X being attached to 
the diaphragm D. Button Y 
presses gentl}^ against X, allow- 
ing a little current to pass 
through the circuit which in- 
cludes a battery, D C, and a re- 
ceiver, R. When D is caused to 
vibrate by the voice, X is made 
to press more or less against Y, 
and this allows more or less 
current to pass through the cir- 
cuit. This dire(5l undulating 
current changes the pull upon 
the diaphragm of R, causing it to vibrate and reproduce 
the original sounds spoken into the transmitter. In 
regular lines, of course, a receiver and transmitter are 
connedted at each end, together with bells, etc., for 
signaling. 

124. Induction Coils in Telephone Work. As the 
resistance of long telephone lines is great, a high eledlric- 
al pressure, or E.M.F., is desired. While the current 
from one or two cells is sufficient to work the transmitter 
properly, and cause undulating currents in the short line, 
it does not have power enough to force its way over a 
long line. 

To get around this difficulty, an induction coil. Fig. 133, 




Fig. 134- 



UofC. 



lOO HOW THE TELEPHONE TRANSMITS SPEECH. 




Fig. 135. 



is used to transform the battery 
current, that flows through the 
carbon transmitter and primary 
coil, into a current with a high 
E. M. F. The battery current 
in the primary coil is undula- 
ting, but always passes in the 
same direction, making the 
magnetic field around the core 
weaker and stronger. This 
causes an alternating current 
in the secondary coil and main 
line. In Fig. 133 P and S rep- 
resent the primary and second- 
ary coils. P is joined in series 
with a cell and carbon trans- 
mitter; S is joined to the distant 
receiver. One end of S can be 
grounded, the current comple- 
ting the circuit through the earth 
and into the receiver through an- 



other wire entering the earth. 
125. Various forms of 

telephones are shown in Figs. 

i34> i35> 136. Fig. 134 
shows a form of desk tele- 
phone ; Fig. 135 show^s a 
common form of wall tele- 
phone ; Fig. 136 show^s head- 
telephones for switchboard 
operators. 




Fig. 136. 



CHAPTER XVII. 



HOW ELECTRICITY IS GENERATED BY DYNAMOS. 

126. The Dynamo, Dyjiaino- Electric Machine or Gen- 
erator, is a machine for converting mechanical energy into , 
an eledlric current, through eledtromagnetic indudlion. 
The dynamo is a machine that will convert steam power, 
for example, into an eledlric current. Stric1:ly speaking, 
a dynamo creates electrical pressure, or electromotive 
force, and not eledtricity, just as a force-pump creates 
water-pressure, and not water. The}^ are generally run 
by steam or water power. 

127. Induced Currents. We have already spoken 





H 



Fig. 137- 



Fig. 138. 



about currents being induced by moving a coil of wire in 
a magnetic field. We shall now see how this principle 
is used in the dynamo which is a generator of induced 
currents. 

Fig. 137 shows how a current can be generated by a 
bar magnet and a coil of wire. Fig. 138 shows how a 
current can be generated by a horseshoe magnet and a 
cofi of wire having an iron core. The ends of the coil are 



lO.? 



BLKCTRICITY GENERATED BY DYNAMOS. 



to be connecfted to an astatic galvanoscope; this forms a 
closed circuit. The coil may be moved past the magnet, 
or the magnet past the coil. 

Fig. 139 shows how a current can be generated by two 



IE 
OB. 



J£ 



H 




Fig. 139. 



Fig. 140. 



coils, H being connedled to an astatic galvanoscope and 
E to a battery. By suddenly bringing E toward H or 
the core of E past that of H, a current is produced. We 
have in this arrangement the main features of a dynamo. 
We can reverse the operation, holding E in one position 





Fig. 141. 



Fig. 142. 



and moving H rapidly toward it. In this case H would 
represent the armature and E the field-magnet. When 
H is moved toward E, the induced current in H flows in 
one diredlion, and when H is suddenly withdrawn from 



ELECTRICITY GENERATED BY DYNAMOS. 



103 



(See ^' Study," Chapter 



^T^? 




E the current is reversed in H. 
XXV., for experiments.) 

128. Induced Currents 
by Rotary Motion. The 

motions of the coils in 
straight lines are not suit- 
able for producing currents 
strong enough for com- 
mercial purposes. In order 
to generate currents of 
considerable strength and 
pressure, the coils of wire 
have to be pushed past 
magnets, or elecftromagnets, 
with great speed. In the 
dynamo the coils are so wound that they can be given 
a rapid rotary motion as they fly past strong eledlro- 

magnets. In this way the 
coil can keep on passing 
the same magnets, in the 
same diredlion, as long as 
force is applied to the shaft 
that carries them. 

129. Field-Magnets ; 
Armature ; Commuta- 
tor. What we need then, 
to produce an induced 
current by a rotary motion, 
is a strong magnetic field, 
a rotating coil of wire 
Fig. 144. properly placed in the 



<> <> ^ ^ 




I04 



EI.KCTRICITY GENERATED BY DYNAMOS. 




Fig. 145. 



field, and some means of leading- the current from the 
machine. 

If a loop of wire, Fig. 140, be so arranged on bearings 

at its ends that it can be made 
to revolve, a current will flow 
through it in one diredlion 
during one-half of the revolu- 
tion, and in the opposite direc- 
tion during the other half, it 
being insulated from all ex- 
ternal conductors. This 
agrees with the experiments 
suggested in § 127, when the 
current generated in a coil 
passed in one diredlion during 
its motion toward the strongest part of the field, and 
in the opposite diredlion when the coil passed out of 
it. A coil must be cut by lines of force to generate a 
current. A current 
inside of the machine, 
as in Fig. 140, would 
be of no value; it must 
be led out to external 
conducflors where it 
can do work. Some 
sort of sliding contadl 
is necessary to connedl 
a revolving condudlor 
with outside stationary ones. The magnet, called \h^ field- 
magnet^ is merely to furnish lines of magnetic force. The 
one turn of wire represents the simplest form of armature. 




Fig. 146. 



EI.ECTRICITY GENERATED BY DYNAMOS. 105 

Fig. 141 shows the ends of a coil joined to two rings, X, 
Y, insulated from each other, and rotating with the coil. 
The two stationary pieces of carbon, A, B, called brushes, 
press against the rings, and to these are joined wires, 
which complete the circuit, and which lead out where the 
current can do work. The arrows show the diredtion of 
the current during one-half of a revolution. The rings 




Fig. 147. 

form a colleSlor, and this arrangement gives an alternating 
current. 

In Fig. 142 the ends of the coil are joined to the two 
halves of a cylinder. These halves, X and Y, are insu- 
lated from each other, and from the axis. The current 
flows from X onto the brush A, through some external 
circuit, to do the work, and thence back through brush 
B onto Y. By the time that Y gets around to A, the 
direcftion of the current in the loop has reversed, so that 
it passes toward Y, but it still enters the outside circuit 



io6 



EI.ECTRICITY GENERATED BY DYNAMOS. 



through A, because Y is then in contadl with A. This 
device is called a commutator^ and it allows a constant or 
direct current to leave the machine. 

In regular machines, the field-magnets are eledlromag- 
nets, the whole or a part of the current from the dynamo 
passing around them on its way out, to excite them and 
make a powerful field between the poles. To lessen the 
resistance to the lines of force on their way from the N to 




Fig. 148. 

the S pole of the field-magnets, the armature coils are 
wound on an iron core; this greatly increases the strength 
of the field, as the lines of force have to jump across but 
two small air-gaps. There are many loops of wire on 
regular armatures, and many segments to the commuta- 
tor, carefully insulated from each other, each getting its 
current from the coil attached to it. 

130. Types of Dynamos. While there is an almost 
endless number of different makes and shapes of dynamos, 



ELECTRICITY GENERATED BY DYNAMOS. 



107 



they may be divided into two great types; the co7iti7iuous 
or direB curreyit, and the alteryiatiiig cicrreiit dynamo. 
Dire6l current machines give out a current which con- 
stantly flows in one direcftion, and this is because a com- 
mutator is used. Alternating currents come from coUedl- 
ors or rings, as shown in Fig. 141; and as an alternating 
current cannot be used to excite the fields, an outside 
current from a small diredl current machine must be 
used. These are called exciters. 

In diredl current machines enough residual magnetism 




Fig. 149. 

is left in the field to induce a slight current in the arma- 
ture when the machine is started. This immediately 
adds strength to the field -magnets, which, in turn, induce 
a stronger current in the armature. 

131. Winding of Dynamos. There are several ways 
of winding dynamos, depending upon the special uses to 
be made of the current. 

The series wound dynamo. Fig. 143, is so arranged that 
the entire current passes around the field-magnet cores 
on its way from the machine. In the shu7it wound dyna- 
mo, Fig. 144, a part, only, of the current from the 



io8 



KLECTRICITY GENERATED BY DYNAMOS. 



machine is carried around the field-magnet cores through 
many turns of fine wire. The compound wotmd dynamo 
is really a combination of the two methods just given. 
In separately-excited dynamos, the current from a sepa- 
rate machine is used to excite the field-magnets. 

132. Various Machines. Fig. 145 shows a hand 
power dynamo which produces a current for experimental 
work. Fig. 146 shows a magneto-eledlrical generator 
which produces a current for medical use. Figs. 147, 
148 show forms of dynamos, and Fig. 149 shows how arc 
lamps are connedled in series to dynamos. 




II 



CHAPTER XVIII. 

HOW THE ELECTRIC CURRENT IS TRANSFORMED. 

133. Electric Current and Work. The amount of 
work a current can do depends upon two factors ; the 
strength (amperes), and the pressure, or E. M. F. (volts). 
A current of 10 amperes with a pressure of 1,000 volts := 
10 X 1,000= 10,000 watts. This furnishes the same 
amount of energy as a current of 50 amperes at 200 volts; 
50 X 200 = 10,000 watts. 

134. Transmission of Currents. It is often neces- 
sary to carry a current a long distance before it is used. 
A current of 50 amperes w^ould need a copper condudlor 
25 times as large (se(5lional area) as one to carry the 10 
ampere current mentioned in § 133. As copper condudl- 
ors are very expensive, eledlric light companies, etc., 
generally try to carry the current on as small a wire as 
possible. To do this, the voltage is kept high, and the 
amperage low. Thus, as seen in § 133, the current of 
1,000 volts and 10 amperes could be carried on a much 
smaller wire than the other current of equal energy. A 
current of 1,000 volts, however, is not adapted for lights, 
etc. , so it has to be changed to lower voltage by some 
form of transformer before it can be used. 

135. Transformers, like indudlion coils, are instru- 
ments for changing the E. M. F. and strength of cur- 
rents. There is very little loss of energy in well-made 
transformers. They consist of tw^o coils of wire on one 

109 



no 



THK ELECTRIC CURRENT TRANSFORMED. 



core; in fact, an inducftion coil may be considered a trans- 
former, but in this a diredl current has to be interrupted. 
If the secondary coil has lOo times as many turns of wire 
as the primary, a current of loo volts can be taken from 
the secondary coil when the primary current is but i 
volt; but the streyigth (amperes) of this new current will 
be but one-hundredth that of the primary current. 

By using the coil of fine wire as the primary, we can 
lower the voltage and increase the strength in the same 
proportion. 

Fig. 150 shows about the simplest form of transformer 




f-p 




Fig. 150. 



Fig. 151. 



with a solid iron core, on which are wound two coils, the 
one, P, being the primary, and the other, S, the secondary. 
Fig. 151 shows the general appearance of one make of 
transformer. The operation of this apparatus, as already 
mentioned, is to reduce the high pressure alternating 
current sent out over the condudlors from the dynamo, 
to a potential at which it can be employed with conveni- 
ence and safety, for illumination and other purposes. 



THE ELECTRIC CURRENT TRANSFORMED. 



Ill 



They consist of two or more coils of wire most carefully 
insulated from one another. A core or magnetic circuit 
of soft iron, composed of very thin punchings, is then 
formed around these coils, the purpose of the iron core 
being to reduce the magnetic resistance and increase the 
indu<5live efTec5l. One set of these coils is connedled with 
the primary or high-pressure wares, while the other set, 
which are called the secondary coils, is connedled to the 




Fig. 152. 



house or low-pressure wires, or wherever the current is 
required for use. The rapidly alternating current im- 
pulses in the primary or high-pressure wires induce sec- 
ondary currents similar in form but opposite in direflion 
in the secondary coils. These current impulses are of a 
much lower pressure, depending upon the ratio of the 
number of turns of wire in the respecftive coils, it being 
customary to wind transformers in such a manner as to 
reduce from 1,000 or 2, 000- volt primaries to 50 or 100- volt 
secondaries, at w^hich voltage the secondary current is 
perfectly harmless. 

136. Motor-Dynamos. Fig. 152. These consist 



112 THE ELECTRIC CURRENT TRANSFORMED. 

essentially of two belt-type machines on a common base, 
diredl coupled together, one machine adling as a motor to 
receive current at a certain voltage, and the other adling 
as a dynamo to give out the current usually at a diflferent 
voltage. As they transform current from one voltage to 
another, motor-dynamos are sometimes called Double 
Field Diredt Current Transformers. The larger sizes 
have three bearings, one bearing being between the two 




Fig- 153. 

machines, while the smaller sizes have but two bear- 
ings, the two armatures being fastened to a common 
spider. 

Applications. The uses to which motor-dynamos are 
put are very various. They are extensively used in the 
larger sizes as ' ' Boosters, ' ' for giving the necessary extra 
force on long elecflric supply circuits to carr}^ the current 
to the end wnth the same pressure as that which reaches 
the ends of the shorter circuits from the station. 

Motor-dynamos have the advantage over dynamotors. 
described later, of having the secondary- voltage easily 



THE ELECTRIC CURRENT TRANSFORMED. II3 

and economically varied over wide rangCvS by means of a 
regulator in the dynamo field. 

137. Dynamotors. Fig. 153. In Dynamotors the 
motor and dynamo armatures are combined in one, thus 
requiring a single field only. The primary armature 
winding, which operates as a motor to drive the machine, 
and the secondary or dynamo winding, which operates as 
a generator to produce a new current, are upon the same 
armature core, so that the armature reacftion of one wind- 
ing neutralizes that of the other. They therefore have 
no tendency to spark, and do not require shifting of the 
brushes with varying load. Having but one field and 
two bearings, they are also more efficient than motor- 
dynamos. 

Applications, They have largely displaced batteries for 
telegraph work. The size shown, occupying a space of 
about 8-inch cube, and having an output of 40 watts, will 
displace about 800 gravity cells, occupying a space of 
about 10 feet cube. The cost of maintenance of such a 
battery per year, exclusive of rent, is about $800, whereas 
the 1-6 dynamotor can be operated at an annual expense 
of $150. 

Dynamotors are largely used by telephone companies 
for charging storage batteries, and for transforming from 
dire(5l to alternating current, for ringing telephone bells. 
Eledlro-cautery, ele(5lroplating, and eledlric heating also 
g^ve use to dynamotors. 



CHAPTER XIX. 

HOW ELECTRIC CURRENTS ARE DISTRIBUTED FOR 

USE. 

138. Conductors and Insulators. To carry the 
powerful current from the generating station to distant 
places where it is to give heat, power, or light, or even 
to carry the small current of a single cell from one 




Fig- 154 



room to another, co7idu6lors must be used. To keep the 
current from passing into the earth before it reaches its 
destination insulators must be used. The form of condudl- 
ors and insulators used will depend upon the current and 




Fig. 156. 

many other conditions. It should be remembered that 
the current has to be carried to the lamp or motor, 
114 



HOW ELECTRIC CURRENTS ARE DISTRIBUTED. II5 



through which it passes, and then back again to the 
dynamo, to form a complete circuit. A break anywhere 




Fig- 157- 

in the circuit stops the current. Insulators are as impor- 
tant as condu(5lors. 

139. Mains, Service Wires, etc. From the switch- 
board the current flows out through the streets in large 
conducflors, or juahis, 
the supply being kept 
up by the dynanios, 
just as water-pressure 
is kept up by the con- 
stant working of 
pumps. Branches, p.^ j^g. 

called service wires, are 
\ led off from the mains to suppl}^ houses or facftories, one 
wire leading the current into the house from one main. 




Il6 HOW ELECTRIC CURRENTS ARE DISTRIBUTED. 



and a similar one leading it out of the house again to the 

other main. 

In large buildings, pairs of wires, called risers, branch 

out from the service 
wires and carry the cur- 
rent up through the 
building. These have 
still other branches — 
Jloor viaiiis, etc., that 
pass through halls, etc. , 
smaller branches finalh' 
reaching the lamps. The 

sizes of all of these wires depend upon how much current 

has to pass through them. The mains in large cities are 




Fig. i59« 




'^^.^^;-:i?^; 





Fig. i6o. 



usually placed underground. In some ])laces they are 
carried on poles. 

140. Electric Conduits are underground passages for 




Fig, i6i. 



HOW ELECTRIC CURRENTS ARE DISTRIBUTED. II7 



eledtric wires, cables, etc. There are several ways of in- 
sulating the conducflors. Sometimes they are placed in 
earthenware or iron 
tubes, or in wood 
that has been treated 
to make it water- 
proof. At short dis- 
tances are placed 
man-holes, where the 





Fig. 162. 



different lengths are joined, and where branches are 

attached. 

Fig. 154 shows creo- 
soted wooden pipes; Fig. 
155 shows another form of 
wooden pipe. Fig. 156 
shows a coupling-box used 
to join Edison tubes. The 
three wires, used in the 
three- wire s^'stem, are in- 
sulated from each other, 
the whole being sur- 
rounded by an iron pipe 
of convenient length for 
handling. Fig. 157 
shows sedlions of man- 
holes and various devices 
used in conduit work. 

141. Miscellaneous 
Appliances. When the 
current enters a house 

for incandescent lighting purposes, for example, quite a 




Fig. 163. 



Il8 HOW El^ECTRIC CURRENTS ARE DISTRIBUTED. 



number of things are necessary. To measure the cur- 
rent a meter is usually placed in the cellar. In new 
houses the insulated condudlors are usually run through 

some sort of tube which 
a(5ls as a double pro- 
tedlion, all being hidden 
from view. Fig. 158 
shows a short length of 
iron tube with a lining 
of insulating material. 
Wires are often run 
through tubes made of 
rubber and various 
other insulating materials. 

Where the current is to be put into houses after the 
plastering has been done, the wires are usually run 
through viouldings or supported by cleais. Fig. 159 




Fig. 164. 



Q^Q^'''"'^^-:^ 




Fig. 166. 



Fig. 167. 



shows a cross-sedlion of moulding. The insulated wires 
are placed in the slots, which are then covered. 

Fig. 160 shows a form of porcelain cleat. These are 
fastened to ceilings or walls, and firmly hold the insulated 
wires in place. Fig. 161 shows a wood cleat. Fig. 162 



HOW ELECTRIC CURRENTS ARE DISTRIBUTED. II9 

shows small porcelain insulators. These may be screwed 
to walls, etc. , the wire being then fastened to them. Fig. 




Fig. 168. 

163 shows how telegraph wires are supported and 
insulated. Fig. 164 shows how wires may be carried by 
trees and insulated from 



H'""^ ■ /#/\- j_- i^"'^ -^KBMB^ 




^^H^^^ 


mS^mmm^ 


^L^K^ 




\ • " -■"■ ■■ ■ "" 



them. 

142. Safety Devices. 
We have seen that when 
too large a current passes 
through a wire,, the wire 
becomes heated and may 
even be melted. Buildings 
are wared to use certain currents, and if from any cause 
much more current than the regular amount should 
suddenly pass through the service wares into the house, 



Fig. 169. 




Fig. 170. 



I20 HOW ELECTRIC CURRENTS ARE DISTRIBUTED. 

the various smaller wires would become overheated, and 
perhaps melt or start a fire. An accidental short circuit, 
for example, would so reduce resistance that too much 
current would suddenly rush through the wires. There 
are several devices by which the over-heating of wires 
is obviated. 

Fig. 165 shows a safety fuse, or safety eut-out, which 
consists of a short length of easily fusible wire, called 




Figs. 171 to 175. 

fuse zvire, placed in the circuit and supported by a porce- 
lain block. These wires are tested, different sizes being 
used for different currents. As soon as there is any tend- 
ency toward over-heating, the fuse blows ; that is, it 
promptly melts and opens the circuit before any damage 
can be done to the regular conductors. Fig. 166 shows 
a cross-sedlion of ?ifitse phcg that can be screwed into an 
ordinary socket. The fuse wire is shown black. 

Fig. 167 shows difuse li7ik. These are also of fusible 
material, and so made that they can be firmly held under 
screw-heads. For heavy currents fuse ribbons are used. 



HOW ELECTRIC CURRENTS ARE DISTRIBUTED. 121 




Fig. 176. 



or several wires or links may be used side by side. Fig. 
168 shows a fusible rosette. Fig. 169 shows two fuse 
wires fixed between screw-heads, the current passing 
through them in opposite direcftions, 
both sides of the circuit being in- 
cluded. Fig. 170 shows various 
forms of cut-outs. 

143. Wires and Cables are made 
in many sizes. Figs. 171 to 175 show 
various ways of making small con- 
ductors. They are made very flexible, 
for some purposes, by twisting many small copper wires 
together, the whole being then covered with insulating 
material. 

Figs. 176, 177, show secftions of submarine cables. 
Such cables consist of copper conductors insulated with 
pure gutta-percha. These are then surrounded by hempen 

yarn or other elastic material, 
and around the whole are 
placed galvanized iron armor 
wires for protedlion. Each 
core, or conductor, contains a 
condudlor consisting of a 
single copper wire or a strand 
of three or more twisted 
copper wires. 

144. Lamp Circuits. As 
has been noted before, in 
order to have the eledlric current do its work, we must 
have a complete circuit. The current must be brought 
back to the dynamo, much of it, of course, having been 




Fig. 177. 



122 HOW KLECTRIC CURRENTS ARE DISTRIBUTED. 

used to produce light, heat, power, etc. For lighting 
purposes this is accomplished in two principal ways. 

Fig. 178 shows a number of lamps so arranged, *' in 
series," that the same current passes through them all, 



+ •—<£) — Q 



-•—€>■ 




Fig. 17S. 



one after the other. The total resistance of the circuit 
is large, as all of the lamp resistances are added together. 
Fig. 179 shows lamps arranged side by side, or ''in 
parallel," between the two main wires. The current 
divides, a part going through each lamp that operates. 
The total resistance of the circuit is not as large as in 
the series arrangement, as the current has many small 
paths in going from one main wire to the other. Fig. 179 
also shows the ordinary hvo-wire system for incandescent 
lighting, the two main wires having usually a difference 




Fig. 179. 



of potential equal to 50 or no volts. These comparatively 
small pressures require fairly large condu(5lors. 

The Three-Wire System, Fig. 180, uses the current 



HOW EI.ECTRIC CURRENTS ARE DISTRIBUTED. 1 23 



from two dynamos, arranged with three main wires. 
While the total voltage is 220, one of the wires being 




ZI2ZL 



-^^^' ' t t t~ 
t ^ ^ f J I ♦ ♦ 




Fig. 180. 

neutral, no volts can be had for ordinary lamps. This 
voltage saves in the cost of conductors. 

The Alternatmg System, Fig. 181, uses transformers. 
The high potential of the current allows small main wires, 
from which branches can be run to the primary coil of 




^ ^ i w i 



I \ \ \ W 



Fig. 181. 

the transformer. The secondary coil sends out an in- 
duced current of 50 or no volts, while that in the pri- 
j mary may be 1,000 to 10,000 volts. 



CHAPTER XX. 

HOW HEAT IS PRODUCED BY THE ELECTRIC CURRENT. 

145. Resistance and Heat. We have seen that all 
wires and condudlors offer resistance to the ele(5lric cur- 
rent. The smaller the wire the greater its resistance. 
Whenever resistance is offered to the current, heat is pro- 
duced. By proper appliances, the heat of resistance can 
be used to advantage for many commercial enterprises. 

Dynamos are used to 
generate the current 
for heating and light- 
ing purposes. 

Fig. 182 shows how 
the current from two 
strong cells can be 
used to heat a short 
length of very fine 
platinum or German-silver wire. The copper condudlors 
attached to the cells do not offer very much resistance. 

It will be seen from the above that in all elecftrical work 
the sizes of the wires used have to be such that they do 
not overheat. The coils of d^^namos, motors, transform- 
ers, ampere-meters, etc., etc., become somewhat heated 
by the currents passing through them, great care being 
taken that they are properly designed and ventilated so 
that they will not burn out. 

146. Electric Welding. Fig. 183 shows one form of 
eledlric welding machine. The principle involved in 




Fig. 182. 



124 



HEAT PRODUCED BY ELECTRIC CURRENT. 



125 




Fig. 183. 



the art of eledlric welding is that of causing currents of 
eledlricity to pass through the abutting ends of the pieces 
of metal which are to be welded, 
thereby generating heat at the 
point of contacfl, which also be- 
comes the point of greatest re- 
sistance, while at the same time 
mechanical pressure is applied to 
force the parts together. As 
the current heats the metal at 
the jundlion to the welding 
temperature, the pressure follows ml 
up the softening surface until a '""^-SS 
complete union or weld is 
efifedled; and, as the heat is first Fig. 184. 




126 



HKAT PRODUCED BY KI.ECTRIC CURRENT. 



developed in the interior of the parts to be welded, the 
interior of the joint is as efl&ciently united as the visible 
exterior. With such a method and apparatus, it is 
found possible to accomplish not only the common kinds 
of welding of iron and steel, but also of metals which 







Figs. 185 to 189. 



have heretofore resisted attempts at welding, and have 
had to be brazed or soldered. 

The introdudlion of the eledlric transformer enables 
enormous currents to be so applied to the weld as to spend 
their energy just at the point where heating is required. 



HEAT PRODUCED BY ELECTRIC CURRENT. 



127 



They need, therefore, only to be applied for a few seconds, 
and the operation is completed before the heat generated 
at the weld has had time to escape by condudlion to any 
v.ther part. 

Although the quantity of the current so employed in 
the pieces to be welded is enormous, the potential at 
which it is applied is extremely low, not much exceeding 
that of the batteries of cells used for ringing eledlric bells 
in houses. 

147. Miscellaneous Applications. Magneto Blast- 



^W^ 







. Fig. 190. 

ing Machines are now in ver}^ common use for blasting 
rocks, etc. Fig. 184 shows one, it being really a small 
hand dynamo, occup^dng less than one-half a cubic foot 
of space. The armature is made to revolve rapidly 
between the poles of the field-magnet b}^ means of a han- 
dle that works up and down. The current is carried by 
wires from the binding-posts to fuses. The heat gener- 
ated by resistance in the fuse ignites the powder or other 
explosive. 

Ele5lric soldering irons^ flat-irons, teakettles, griddles, 



128 



HEAT PRODUCED BY ELECTRIC CURRENT. 



broilers^ glue pots ^ chafijig -dishes^ stoves, etc., etc., are now 
made. Figs. 185 to 189 show some of these applications. 
The coils for producing the resistance are inclosed in the 
apparatus. 

Fig. 190 shows a complete eledlric kitchen. Any ket- 




Fig. 191. 

tie or part of the outfit can be made hot by simply turn- 
ing a switch. Fig. 191 shows an ele(5lric heater placed 
under a car seat. Many large industries that make use 
of the heating effedls of the current are now being 
carried on. 



I 
t 



CHAPTER XXI. 



HOW LIGHT IS PRODUCED BY THE INCANDESCENT 

LAMP. 



148. Incandescence. 




We have just seen that the 
elecftric current produces heat 
when it flows through a con- 
dudlor that offers considerable 
resistance to it. As soon as 
this was discovered men began 
to experiment to find whether 
a pracflical light could also be 
produced. It was found that 
a w4re could be kept hot by 
constantly passing a current 
through it, and that the light 
given out from it became 




Fig. 192. Fig. 193. 

whiter and whiter as the wire became hotter. The wire 
was said to be incandesceyit, or glowing with heat. As 



130 I<IGHT PRODUCED BY INCANDESCENT LAMP. 



metal wires are good condudlors of eledlricity, they had 
to be made extremely fine to offer enough resistance ; 
too fine, in fa6l, to be properly handled. 

149. The Incandescent Lamp. Many substances 
were experimented upon to find a proper material out of 
which could be made a filament that would 
give the proper resistance and at the same 
time be strong and lasting. It was found 
that hair- like pieces of carbon offered the 
proper resistance to the current. When 
heated in the air, however, carbon bums; so 
it became necessary to 
place the carbon fila- 
ments in a globe from 
which all the air had 
been pumped before 




\ 



.;! 






P...... 




Fig. 194. 



Fig. 195. 



Fig. 196. 



passing the current through them. This proved to be a 
success. 

Fig. 192 shows the ordinary form of lamp. The carbon 
filament is attached, by carbon paste, to short platinum 
wires that are sealed in the glass, their lower ends being 
connedled to short copper wires that are joined to the 



UGHT PRODUCED BY INCANDESCENT LAMP. 131 

terminals of the lamp. When the lamp is screwed into 
its socket, the current can pass up one side of the fila- 
ment and down the other. The filaments used have been 




Fig. 197. 

made of every form of carbonized vegetable matter. 
Bamboo has been largely used, fine strips being cut by 
dies and then heated in air-tight boxes containing fine 
carbon until they were thoroughly carbonized. This 
baking of the bamboo produces a tough fiber of carbon. 
Various forms of thread have been carbonized and used. 
Filaments are now made by pressing finely pulverized 
carbon, with a binding material, through small dies. The 
filaments are made of such sizes and lengths that will 
adapt them to the particular current with which they are 
to be used. The longer the filament, the greater its 
resistance, and the greater the voltage necessary to push 
the current through it. 

After the filaments are properly attached, the air is 




Fig. 198. 

( pumped from the bulb or globe. This is done with some 
j formof mercury pump, and the air is so thoroughly re- 
moved from the bulb that about one-millionth only of the 



132 LIGHT PRODUCED BY INCANDKSCEJNT I^AMP. 




Fig. 199. 

original air remains. Before sealing oflF the lamp, a cur- 
rent is passed through the filament to drive out absorbed 
air and gases, and these are carried 
away by the pump. By proper treat- 
ment the filaments have a uniform 
resistance throughout, and glow uni- 
formly when the current passes. 

150. Candle-Power. A lamp is 
said to have 4, 8, 16 or more candle- 
power. A i6-candle-power lamp, for 
example, means one that will give as 
much light as sixteen standard 
candles. A standard sperm candle 
burns tw^o grains a minute. The 
candle-power of a lamp can be in- 
creased by forcing a strong current 
through it, but this shortens its life. 

The Ctirre7it used for incandescent 

lamps has to be strong enough to 

force its way through the filament and 

Fig. 200. produce a heat sufficient to give a 




UGHT PRODUCED BY INCANDESCENT LAMP. 1 33 

good light. The usual current has 50 or no volts, 
although small lamps are made that can be run by two 
or three cells. If the voltage of the current is less than 
that for which the lamp was made, the light will be dim. 
The filament can be instantly burned 
out by passing a current of too high 
pressure through it. 

Even with the proper current, 
lamps soon begin to deteriorate, as 
small particles of carbon leave the 
filament and cling to the glass. 
This is due to the evaporation, 
and it makes the filament smaller, and a higher pressure 
is then needed to force the current through the increased 
resistance; besides this, the darkened bulb does not prop- 
erly let the light out. The current may be direct or 
alternating. 

151. The Uses to which incandescent lamps are put 




Fig. 201. 




Fig. 202. 



are almost numberless. Fig. 193 shows a decorative 
lamp. Fancy lamps are made in all colors. Fig. 194 
shows a conic candle lamp, to imitate a candle. What 
corresponds to the body of the candle (see figure B to C) 



134 LIGHT PRODUCED BY INCANDESCENT LAMP. 



is a delicately tinted opal glass tube surmounted (see 
figure A to B) by a finely proportioned conic lamp with 
frosted globe. C to D in the figure repre- 
sents the regular base, and thus the relative 
proportions of the parts are shown. Fig. 





Fig. 203. 

195 shows another form of candelabra lamp. Fig. 196 
shows small dental lamps. V\g. 197 vshows a small lamp 

with mirror for use in the throat. 
Fig. 198 shows lamp with half 
shade attached, used for library 
tables. Fig. 199 shows an 
elecT;ric pendant for several 
lamps, with shade. Fig. 200 
shows a lamp guard. Fig. 201 
shows a lamp socket, into which 
the lamp is screwed. Fig. 202 
shows incandescent bulbs joined 
in parallel to the + and — mains. 
Fig. 203 shows how the lamp 
cord can be adjusted to desired 
length. Fig. 204 shows a lamp with refle(5lor placed on 
a desk. Fig. 205 shows a form of shade and refledtor. 




Fig. 205. 



CHAPTER XXII. 



HOW LIGHT IS PRODUCED BY THE ARC LAMP. 

152. The Electric Arc. When a strong current 
passes from one carbon rod to another across an air- 
space, an eleS27'ic arc is pro- 
duced. When the ends of 
two carbon rods touch, a 
current can pass from one 
to the other, but the im- 
perfedl contadl causes re- 
sistance enough to heat the 
ends red-hot. If the rods 
be separated slightly, the 
current will continue to 
flow, as the intensely heated 
air and flying particles of 
carbon reduce the resist- 
ance of the air-space. 

Fig. 206 shows two car- 
bon rods w^hich are joined 
to the tw^o terminals of a 
dynamo. The upper, or 
positive, carbon gradually 
wears away and becomes 
slightly hollow. The 
heated crater^ as it is called, is the hottest part. The 
negative carbon becomes pointed. The arc will pass in 
a vacuum, and even under water. 

135 




Fig. 206. 



136 



HOW LIGHT IS PRODUCED BY ARC LAMPS. 



As the eledlric arc is extremely hot, metals are easily 
vaporized in it; in fadl, even the carbon rods themselves 
slowly melt and vaporize. This extreme heat is used for 
many industrial purposes. 

' ' The phenomenon of the elecftric arc was first noticed by 
Humphrey Davy in 1800, and its ex- 
planation appears to be the following: 
"^ Before conta(5l the difference of poten- 
tial between the points is insufficient 
to permit a spark to leap across even 
,^U-s of an inch of air-space, but when 





Fig. 208. 



.11 



the carbons are made to touch, a current is established. 
On separating the carbons, the momentary extra current 
due to self-indudlion of the circuit, w^hich possesses a high - - 
eledlromotive force, can leap the short distance, and inf 1 
doing so volatilizes a small quantity of carbon between 



HOW LIGHT IS PRODUCED BY ARC I<AMPS. 1 37 




Fig. 209. 



the points. Carbon vapor, being a partial condudlor, 

allows the current to continue to flow across the gap, 

provided it be not too wide ; but as 

the carbon vapor has a very high re- 
sistance it becomes intensely heated 

by the passage of the current, and the 

carbon points aLso grow hot. Since, 

however, solid matter is a better 

radiator than gaseous matter, the 

carbon points emit far more light 

than the arc itself, though they are 

not so hot. It is observed, also, that 

particles of carbon are torn away 

from the + eledlrode, which becomes 

hollowed out to a cup-shape, and 

some of these are deposited on the — eledlrode. ' ' 

153. Arc Lamps. As the carbons gradually wear 

away, some device is necessary to keep their ends the 
right distance apart. If they 
are too near, the arc is very 
small ; and if too far apart, 
the current can not pass and 
the light goes out. The 
positive carbon gives the more 
intense light and wears away 
about twice as fast as the — 
carbon, so it is placed above 
the — carbon, to throw the 
light downwards. 
Arc lamps contain some device by which the proper 

distance between the carbons can be kept. Most of them 





Fig. 210. 



Fig. 211. 



138 



HOW LIGHT IS PRODUCED BY ARC LAMPS. 



grip the upper carbon and pull 
it far enough above the lower 
one to evStablish the arc. As 
soon as the distance between 
them gets too great again, the 
grip on the upper carbon is 
loosened, allowing the carbon to 
drop until it comes in contadl 
with the lower one, thus starting 
the current again. These 
motions are accomplished byB I 
electromagnets. Fig. 207 shows 

a form of arc lamj) with single carbons that will bum 

from 7 to 9 hours. 




Fig. 212. 





Fig. 213. 



Fig. 214, 



HOW LIGHT IS PRODUCED BY ARC LAMPS. 



139 



Fig. 208 shows the mechanism by which the carbons 
are regulated. Fig. 209 shows a form of double carbcni, 
or all-night lamp, one set of carbons being first used, the 




Fig. 215. 



other set being automaticall}' switched in at the proper 
time. 

Figs. 210, 211 show forms of short arc lamps, for use 
under low ceilings, so common in basements, etc. 

Fig. 212 shows a hand-feed foc2issmg t3^pe of arc lamp. 
In regular street lamps, the upper carbon only is fed by 
mechanism, as it burns away about twice as fast as the 
lower one, thus bringing the arc lower and lower. WTien 



140 HOW I^IGllT IS PRODUCED BY ARC LAMPS. 

it is desired to keep the arc at the focus of a refledlor, 
both carbons must be fed. 

Fig. 213 shows a theatre arc lamp^ used to throw a 
strong beam of light from the balcony to the stage. 

Fig. 214 shows the arc lamp used as a search-light. 
The reflecftor throws a powerful beam of light that can be 
seen for miles; in fadl, the light is used for signalling at 
night. Fig. 215 shows how search-lights are used at 
night on war-vessels. 



CHAPTER XXIII. 

X-RAYS, AND HOW THE BONES OF THE HUMAN BODY 
ABE PHOTOGRAPHED. 



154. Disruptive Discharges. We have seen, in the 

study of induction coils, that a spark can jump several 
inches between the terminals of the secondar}' coil. The 
attraction between the two oppositely charged terminals 




Fig. 216. 

gets so great that it overcomes the resistance of the air- 
space between them, a brilliant spark passes, and they are 
discharged. This sudden discharge is said to be disrupt- 
ive, and it is accompanied by a flash of light and a loud 
report. T\iQ,path of the discharge may be nearly straight, 

141 



142 



X-RAYS — HUMAN BONES PHOTOGRAPHED. 



or crooked, depending upon the nature of the material in 
the gap between the terminals. 
155. Effect of Air Pressure on Spark. The dis- 




Fig. 218. 

ruptive spark takes place in air at ordinary pressures. 
The nature of the spark is greatly changed when the pres- 
sure of the air decreases. Fig. 2 1 6 shows an air-tight glass 

tube so arranged that the 
air can be slowly removed 
with an air-pump. The 
upper rod shown can be 
raised or lowered to in- 
crease the distance between 
it and the lower rod, these 
adling as the terminals of 
an induction coil. Before exhausting any air, the spark 
will jump a small distance between the rods and ac5l as 
in open air. As soon as a small amount of air is re- 




Fig. 219. 



X-RAYS — HUMAN BONES PHOTOGRAPHKD. 



143 



moved, a change takes place. The spark is not so in- 
tense and has no definite path, there being a general 
glow throughout the tube. As the air pressure becomes 
still less, the glow becomes brighter, until the entire tube 
is full of purple light that is able to pass the entire 
length of it; that is, the discharge takes place better in 
rarefied air than it does in ordinary air. 

156. Vacuum-Tubes. As elecT:ricity passes through 

rarefied gases much easier than 

_ _ through ordinary air, regular 

^ MLM^ tubes, called vacuum-tubes, are 






Fig. 220-A. 

made for such study. Fig. 217 shows a plain tube of 
this kind, platinum terminals being fused in the glass 
for connedlions. These tubes are often made in com- 
plicated forms, Fig. 218, with colored glass, and are 
, called Geissler tubes. They are often made in such a 
' way that the eledlrodes are in the shape of discs, etc. , 
and are called Crookes tubes, Fig. 219. A slight amount 
of gas is left in the tubes. 
I 157. Cathode Rays. The cathode is the eledlrode of 



144 



X-RAYS — HUMAN BONES PHOTOGRAPHED. 



a vacuum-tube by which the current leaves the tube, and 
it has been known for some time that some kind of influ- 
ence passes in straight lines from this point. Shadows, 
Fig. 219, are cast by such rays, a screen being placed in 
their path. 

158. X-Rays. Professor Roentgen of Wiirzburg dis- 
covered that when the cathode rays are allowed to fall 




Fig. 221. 

upon a solid body, the solid body gives out still other rays 
which differ somewhat from the original cathode rays. 
They can penetrate, more or less, through many bodies that 
are usually considered opaque. The hand, for example, 
may be used as a negative for producing a photograph of 
the bones, as the rays do not pass equally well through 
flesh and bone. 



X-RAYS — HUMAN BONES PHOTOGRAPHED. 



H5 



Fig. 2 20 shows a Crookes tube fitted with a metal plate, 
so that the cathode rays coming from C will strike it. 
The X-rays are given out from P. These rays are 




Fig. 222. 

invisible and are even given out where the cathode rays 
strike the glass. Some chemical compounds are made 
luminous by these rays; so screens are made and coated 
with them in order that the shadows produced by the 




Fig. 223. 

X-rays can be seen by the eye. Professor Roentgen 
named thCvSe the X-rays. Fig. 2 20- A shows 2, fluoroscope 
that contains a screen covered with proper chemicals. 



146 X-RAYS — HUMAN BONES PHOTOGRAPHED. 

159. X-Ray Photographs. Bone does not allow the 
X-rays to pass through it as readily as flesh, so if the 
hand be placed over a sensitized photographic plate, Fig. 
221, and proper connexions be made with the indudlion 
coil, etc., the hand acfls as a photographic negative. 
Upon developing the plate, as in ordinary photography, a 
pidlure or shadow of the bones will be seen. Fig. 222 
shows the arrangement of battery, indudlion coil, focus 
tube, etc., for examining the bones of the human body. 

Fig. 223 shows the bones of a fish. Such photographs 
have been very valuable in discovering the location of 
bullets, needles, etc., that have become imbedded in the 
flesh, as well as in locating breaks in the bones. 



CHAPTER XXIV. 

THE ELECTRIC MOTOR, AND HOW IT DOES WORK. 

l6o. Currents and Motion. We have seen, Chapter 
XII., that when coils of wire are rapidly moved across a 




Fig. 224. 

strong magnetic field, a current of eledlricity is generated. 
We have now to deal with the opposite of this ; that is, 
we are to study how motion can be produced by allowing 




Fig. 225. 



a current of eledlricity to pass through the armature of a 
machine. 

H7 



148 THE EI.ECTRIC MOTOR, AND HOW IT WORKS. 

Fig. 224 shows, by diagram, a coil H, suspended so 
that it can move easily, its ends being joined to a cur- 
rent reverser, and this, in turn, to a dry cell DC. A 
magnet, H M, will attradl the core of H when no current 
passes. When the current is allowed to pass first in one 
direcftion and then in the opposite diredlion, by using the 
reverser, the core of H will jump back and forth from one 




Fig. 226. 

pole of H M to the other. There are many ways by 
which motion can be produced by the current, but to 
have it practical, the motion must be a rotary one. (See 
''Study," Chapter XXVI., for numerous experiments.) 
161. The Electric Motor is a machine for transform- 
ing eledlric energy into mechanical power. The construc- 
tion of motors is very similar to that of dynamos. They 
have field-magnets, armature coils, commutator, etc. ; in 



THE ELECTRIC MOTOR, AND HOW IT WORKS. 1 49 

fact, the armature of an ordinary direct current dynamo 
will revolve if a current be passed through it, entering by 
one brush and leaving by the other. There are many 
little differences of construction, for mechanical and elec- 
trical reasons, but we may say that the general construc- 
tion of dynamos and motors is the same. 

Fig. 225 shows a coil of wire, the ends of which are 
connected to copper and zinc plates. These plates are 




Fig. 227. 



floated in dilute sulphuric acid, and form a simple cell 
which sends a current through the wire, as shown by the 
arrows. 

We have seen that a current-carrjang wire has a mag- 
netic field and adls like a magnet; so it will be easily seen 
that if a magnet be held near the wire it will be either 
attradled or repelled, the motion depending upon the 
poles that come near each other. As shown in the figure, 
the N pole of the magnet repels the field of the wire, 



I50 THE ELECTRIC MOTOR, AND HOW IT WORKS. 



causing it to revolve. We see that this adtion is just the 
reverse to that in galvanometers, where the coil is fixed, 
and the magnet, or magnetic needle, is allowed to move. 

As soon as the part of the 

wire, marked A in Fig. 

225, gets a little distance 

from the pole, the opposite 

side of the wire, B, begins 

to be attra(5led by it, the 

attracflion getting stronger 

and stronger, until it gets 

opposite the N pole. If 

the N pole were still held 

in place, B would vibrate 

back and forth a few times, and finally come to rest 

near tlie pole. If, however, as soon as B gets opposite 

N the S pole of the magnet be quickly turned toward 




Fig. 228. 




Figs. 229 to 231. 

B, the coil will be repelled and the rotar>'' motion will 
continue. 

Let us now see how this helps to explain elecflric mo- 



«| 



THE ELECTRIC MOTOR, AND HOW IT WORKS. 151 



tors. We may consider the wire of Fig. 225 as one coil 
of an armature, and the plates, C and Z, as the halves of 
a commutator. In this arrangement, it must be noted, 
the current always flows through the armature coil in the 
same diredlion, the rotation 
being kept up by reversing 
the poles of the field- 
magnet. In ordinary simple 
motors the current is re- 
versed in the armature 
coils, the field-magnets re- 
maining in one position 
without changing the poles. 
This produces the same effedt as the above. The 
current is reversed automatically as the brushes allow 




Fig. 232. 




Fig. 233. 



the current to enter first one commutator bar and then 
the opposite one as the armature revolves. The regular 



152 THE KI.KCTRIC MOTOR, AND HOW IT WORKS. 



armatures have many coils and many commutator bars, 
as will be seen by examining the illustrations shown. 
The ordinary galvanometer may be considered a form 
of motor. By properly opening 
and closing the circuit, the rotary 
motion of the needle can be kept 
up as long as current is supplied. 
Even an eledlric bell or telegraph 
sounder may be considered a 
motor, giving motion straight for- 
ward and back. 

162. The Uses of Motors are 
many. It would be impossible to 
mention all the things that are 
done with the power from motors. 
A few illustrations will give an 
idea of the way motors are attached 
to machines. 

Fig. 226 shows one form of 
motor, the parts being shown in 
Fig. 227. 

Fig. 228 shows a fan motor run 

by a battery. They are generally 

run by the current from the street. 

Figs. 229-231 show other forms of 

fan motors. Fig. 232 shows an 

eledlric hat polisher. A church 

organ bellows is shown in Fig. 233, so arranged that it 

can be pumped by an eledlric motor. Fig. 234 shows a 

motor diredl connecfted to a drill press. 

163. Starting Boxes. If too much current were 




THE ELECTRIC MOTOR, AND HOW IT WORKS. 1 53 



suddenly allowed to pass into the armature of a motor, 
the coils would be over-heated, and perhaps destroyed, 
before it attained its full speed. A rapidly revolving 
armature will take more current, without being over- 
heated, than one not in motion. A motor at full speed 
adls like a dynamo, and generates a current which tends 
to flow from the machine in a direcftion opposite to that 
which produces the motion. It is evident, then, that 
when the armature is at rest, all the current turned on 





Fig. 235. 



Fig. 236. 



passes through it without meeting with this opposing 
current. 

Fig- 235 shows a starting, stopping, and regulating 
box, inside of which are a number of German-silver re- 
sistance coils properly connecfted to contadl-points at the 
top. By turning the knob, the field of the motor is im- 
mediately charged first through resistance, then direcfl, 
and then the current is put on the armature gradually 
through a series of coils, the amount of current depend- 
ing upon the distance the switch is turned. Fig. 236 
shows a cross- sedlion of the same. 



CHAPTER XXV. 



ELECTRIC CARS, BOATS, AND ATJTOMOBIIiES, 

164. Electric Cars, as well as boats, automobiles, etc., 
etc., are moved by the power that comes from eledlric 
motors, these receiving current from the dynamos placed 
at some "central station." We have already seen how 
the motor can do many kinds of work. By properly 
gearing it to the car wheels, motion can be given to them 
which will move the car. 

Fig. 237 shows two dynamos which will be supposed to 




Fig. 237. 

be at a power house and which send out a current to 
propel cars. From the figure it will be seen that the 
wires over the cars, called trolley- wires, are connected to. 
the positive (+) terminals of the dynamos, and that the 
negative ( — ) terminals are connedled to the tracks. In 
case a wire were allowed to join the trolley- wire and 
track, we should have a short circuit, and current would 
not only rush back to the dynamo without doing useful 
154 



ELECTRIC CARS, BOATS, AND AUTOMOBILES. 1 55 



work, but it would probably injure the machines. When 
some of the current is allowed to pass through a car, 
motion is produced in the motors, as has been explained. 
As the number of cars increases, more current passes back 
, to the dynamos , which must 

do more work to furnish 
such current. 

Ti'olley-poles, fastened to 
the top of the cars and 
which end in grooved 
wheels, qsII^A trolley-wheels, 
are pressed by springs 
against the trolley-wires. 
The current passes down 
these through switches to 
controllers at each end of 
the car, one set being used 
at a time. 





Fig. 238. 



Fig. 239. 



165. The Controllers, as the name suggests, control 
the speed of the car by allowing more or less current to 
pass through the motors. The motors, resistance coils 
and controllers are so connecfted with each other that 
the amount of current used can be regulated. 



156 EI.KCTRIC CARS, BOATS, AND AUTOMOBII.ES. 



When the motorman turns the handle of the controller 
to the first notch, the current passes through all of the 
resistance wires placed under the car, then through one 




Fig. 240. 

motor after the other. The motors being joined in 
series by the proper connedlions at the controller, the 
greatest resistance is offered to the current and the car 
runs at the slowest speed at this first notch. As more 
resistance is cut out by turning the handle to other 
notches, the car in- 
creases its speed ; but 
as the resistance wires 
become heated and the 
heat passes into the 
air, there is a loss of 
energy. It is not 
economical to run a 
car at such a speed ][^"'. 
that energy is wasted 
as heat. As soon as 




Fig. 241. 



the resistance is all cut out, the current simply passes 
through the motors joined in series. This gives a fairly 



ELECTRIC CARS, BOATS, AND AUTOMOBILES. 1 57 



slow speed and one that is economical because all the 
current tends to produce motion. 

By allowing the current to pass through the motors 
joined in parallel, that is, by allowing each to take a part 





Fig. 242. 



Fig. 243. 



of the current, the resistance is greatly reduced, and a 
higher speed attained. This is not instantly done, how- 
ever, as too much strain would be put upon the motors. 
As soon as the next notch is reached, the motors are 
joined in parallel and the resistance also thrown in again. 
By turning the handle still more, resistance is gradually 
cut out, and the highest speed produced when the current 
passes only through the motors in parallel. 

Fig. 238 represents a controller, by diagram, showing 
the relative positions of the controller cylinder, reversing 
and cut-out cylinders, arrangements for 
blowing out the short eledlric arcs 
formed, etc. A ratchet and pawl is pro- 
vided, which indicates positively the run- 
ning notches, at the same time permitting 
the cylinder to move with ease. Fig. 
2 39 shows a top view of the controller. 

166. Overhead and Underground Systems. When 
wires for furnishing current are placed over the tracks, as 




Fig. 244. 



158 KI.KCTRIC CARS, BOATS, AND AUTOMOBILES. 

in Fig. 237, we have the overhead system. In cities the 
underground system is largely used. The location of the 
conducing wires beneath the surface of the street removes 
all danger to the public, and protedls them from all inter- 
ference, leaving the street free from poles and wires. 

Fig. 240 shows a cross-sedlion of an underground con- 
duit. The rails, R R, are supported by cast-iron yokes, A, 
placed five feet apart, and thoroughly imbedded in con- 
crete. The conduit has sewer connedlions every 100 feet. 
Condudling bars, C C, are placed on each side of the con- 
duit, and these are divided into se(5lions of about 500 




Fig. 245- 



% 



feet. Insulators, D D, are placed every 15 feet. They 
are attached to, and direcflly under, the slot-rails, the _ 
stem passing through the conducftor bar. ^ 

Figs. 240 and 241 show the plow E. The contaA 
plates are carried on coiled springs to allow a free motion. 
Two guide-wheels, F F, are attached to the leg of the plow. 
The conducfting wires are carried up through the leg of 
the plow. 

167. Appliances. A large number of articles are 
needed in the construction of elecftric railroads. A few, & 
only, can be shown that are used for the overhead system. * 
Fig. 242 shows a pole insulator. Fig. 243 shows a feeder- 
wire insulator. Fig. 244 shows a line suspension. Fig. W 
245 shows a form of right-angle cross which allows the 



KLECTRIC CARS, BOATS, AND AUTOMOBII.ES. 159 

trolley-wheels of crossing lines to pass. Fig. 246 shows 
a switch. In winter a part of the current is allowed to 
pass through eledlric heaters placed under the seats of 
eledlric cars. 

168. Electric Boats are run by the current from 
storage batteries which are usually placed under the 
seats. An elecftric motor large enough to run a small 
boat takes up very little room and is generally placed 




' Fig. 246. 

under the jBioor. This leaves the entire boat for the use 
of passengers. The motor is connected to the shaft that 
turns the screw. Fig. 247 shows one design. 

169. Electric Automobiles represent the highest type 
of eledlrical and mechanical construdlion. The running- 
gear is usually made of the best cold-drawn seamless 
steel tubing, to get the greatest strength from a given 
weight of material. The wheels are made in a variety 
of styles, but nearly all have ball bearings and pneumatic 
tires. In the lightest styles the wheels have wire spokes. 

The ele5lric motors, supported by the running-gear, are 



l6o ELECTRIC CARS, BOATS, AND AUTOMOBILES. 

geared to the rear wheels. The motors are made as 
nearly dust-proof as possible. 

Storage batteries are put in a convenient place, depend- 
ing upon the design of the carriage, and from these the 
motors receive the current. These can be charged from 
the ordinary no- volt lighting circuits or from private 
dynamos. The proper plugs and attachments are usually 
furnished by the various makers for connedling the 




Fig. 247. 



batteries with the street current, which is shut off when 
the batteries are full by an automatic switch. 

Controllers are used, as on elecflric cars, the lever for 
starting, stopping, etc., being usually placed on the left- 
hand side of the seat. The steering is done by a lever 
that moves the front wheels. Strong brakes, and the 
ability to quickly reverse the motors, allow elecflric car- 
riages to be stopped suddenly in case of accidents. 

Eledlric automobiles are largely used in cities, orw^here 
the current can be easily had. The batteries must be 
re-charged after they have run the motors for a certain 
time which depends upon the speed and road, as well as 



ELECTRIC CARS, BOATS, AND AUTOMOBILES. l6l 

Upon the construdlion. Where carriages are to be run 
ahnost constantly, as is the case with those used for general 
passenger service in cities, duplicate batteries are neces- 




Fig. 248. 

sary , so that one or two sets can be charged while another 
is in use. Fig. 248 shows one form of eledlric vehicle, 
the storage batteries being placed under and back of the 
seat. 



CHAPTER XXVI. 



A WORD ABOUT CENTRAL STATIONS. 



170. Central Stations, as the word implies, are places 
where, for example, eledlricity is generated for the incan- 
descent or arc lights used in a certain neighborhood ; 
where telephone or telegraph messages 
are sent to be resent to some other station; 
where operators are kept to switch dif- 
ferent lines together, so that those on 
one line can talk to those on another, 
etc. , etc. There are many kinds of cen- 
tral stations, each requiring a large 
amount of special apparatus to carry on 
the work. Fig. 249 gives a hint in 
regard to the way car lines get their 
power from a central power station. 
As a large part of the apparatus required 
in ordinary central stations has already 
been described, it is not necessary to go 
into the details of such stations. 

In lighting stations, for example, we 
have three principal kinds of apparatus. 
Boilers produce the steam that runs the 
steam engines, and these run the dyna- 
mos that give the current. Besides these there are many 
other things needed. The eledlrical energy that goes over 
the wires to furnish light, heat, and power, really comes 
indirec5lly from the coal that is used to boil water and 




Fig. 249. 



162 



A WORD ABOUT CENTRA!, STATIONS. 



163 




Fig. 250. 




Fig. 251. 

! convert it into steam. The various parts of the central 
station merely aid in this transformation of energy. 

The dynamos are connedled to the engines by belts, or 



1 64 A WORD ABOUT CENTRAL STATIONS. 

they are diredl connedled. Figs. 250, 251, show dynamos 
connec5led to engines without belts. 

The current from the dynamos is led to large switch- 
boards which contain switches, voltmeters, ammeters, 
lightning arresters, and various other apparatus for the 
proper control and measurement of the current. From 
the switchboard it is allowed to pass through the various 
street mains, from which it is finally led to lamps, motors, 
etc. 

Water-power is frequently used to drive the dynamos 
instead of steam engines. The water turns some form of 
water-wheel which is connec5led to the dynamos. At 
Niagara Falls, for example, immense quantities of current 
are generated for light, heat, power, and industrial pur- 
poses. 




CHAPTER XXVII. 

MISCELLANEOUS USES OF ELECTRICITY, 

171. The Many Uses to which the elecftric current is 
put are almost numberless. New uses are being found 
for it every day. Some of the common applications are 
given below. 

172. Automatic Electric Program Clocks, Fig. 





Fig. 252. 



Fig. 253. 



252, are largely used in all sorts of establishments, schools, 
etc., for ringing bells at certain stated periods. The 
lower dial shown has many contadl-points that can be 
inserted to correspond to given times. As this revolves, 
the circuits are closed, one after the other, and it may be 
so set that bells will be rung in different parts of the 
house every five minutes, if desired. 

173. Call Boxes are used to send in calls of various 

165 



1 66 



MISCELLANEOUS USES OF ELECTRICITY. 



kinds to central stations. Fig. 253 shows one form. The 
number of different calls provided includes messenger, car- 
rier, coupe, express wagon, dodlor, laborer, police, fire, 
together with three more, which may be made special to 
suit the convenience of the individual customer. The 
instruments are provided with apparatus for receiving a 
return signal, the objedt of which is to notify the sub- 





Fig. 254- 



Fig. 255. 



scriber that his call has been received and is having 
attention. 

Fig. 254 shows another form of call box, the handle 
being moved around to the call desired. As it springs 
back to the original position, an interrupted current 
passes through the box to the central station, causing a 
bell to tap a certain number of times, giving the call and 
location of the box. 

174. Electric Gas-Lighters. Fig. 255 shows a 
ratchet biiryier. The first pull of the chain turns on the 
gas through a four- way gas-cock, governed by a ratchet- 



MISCKLI.ANKOUS USES OF ELECTRICITY. 



167 



wheel and pawl. The issuing gas is lighted by a wipe- 
spark at the tip of the burner. Alternate pulls shut off 
the gas. As the lever brings the attached wire A, in con- 
tadl with the wire B, a bright spark passes, which ignites 
the gas, the burner being joined with a battery and in- 
duction or spark coil. 

Automatic burners are used when it is desired to light 
gas at a distance from the push-button. Fig. 256 shows 





Fig. 256. 



Fig. 257. 



one form. Two eledlromagnets are shown, one being 
generally joined to a while push-button for turning on 
the gas and lighting it, the other being joined to a black 
button which turns off the gas when it is pressed. The 
armatures of the magnets work the gas-valve. Sparks 
ignite the gas, as explained above. 

175. Door Openers. Fig. 257 shows one form. 
They contain eledlromagnets so arranged that when the 



i68 



MISCBLI.ANEOUS USKS OF ELECTRICITY. 



armature is attradled by the pushing of a button any- 
where in the building, the door can be pushed open. 

176. Dental Outfits. Fig. 258 shows a motor 
arranged to run dental apparatus. The motor can be 
connedled to an ordinary incandes- 
cent light socket. In case the cur- 
«^ i I rent gives out, the drills, etc., can 

y ^JL ^ be run by foot power. 

177. Annunciators of various 
kinds are used in hotels, facftories, 





etc., to indicate a certain room 

when a bell rings at the office. 

The bell indicates that some one 

has called, and the annunciator 

shows the location of the call by 

displaying the number of the room 

Fig. 258. or its location. Fig. 259 shows a 

small annunciator. They contain 

elec5lromagnets which are connedled to push-buttons 

located in the building, and which bring the numbers 

into place as soon as the current passes through them. 



INDEX.. 



Numbers refer to paragraphs. See Table of Contents for the 
titles of the various chapters. 



Action of magnets upon each 
other, 32. 

Adjuster, for lamp cords, 151. 

Air pressure, effect of spark 
upon, 155. 

Alumimim-leaf, for electro- 
scopes, 5. 

Alternating current, 129, 130; 
system of wiring for, 144. 

Amalgamation of zincs, 47. 

Amber, electrification upon, 3. 

Ammeter, the, 74: 

how placed in circuit, 77. 

Ampere, the, 72. 

Annunciators, 177. 

Anode, 79, 82. 

Apparatus for electrical 
measurements, Chap. VI. 

Appliances, for distribution of 
currents, 141; 
for electric railways, 167; 
for heating by electricity, 

147. 
Arc, the electric, 152. 
Arc lamp, the, 153; 

how light is produced by, 

Chap. XXII.; 
double carbon, 153; 
hand-feed focussing, 153; 
for search-lights, 153; 
short, for basements, 153; 



single carbon, 153; 

for theater use, 153. 
Armature, of dynamo, 127, 129; 

of electromagnets, 98; 

of horseshoe magnet, 26; 

of motors, 161; 

uses of, 39. 
Artificial magnets, 25. 
Astatic, detectors, 94; 

galvanometer, 73; 

needles, 94. 
Aurora borealis, 23. 
Automatic, current inter- 
rupters, 104, 115; 

gas lighters, 174; 

program clocks, 172. 
Automobiles, 169; 

controllers for, 169; 

motors for, 169; 

steering of, 169; 

storage batteries for, 169. 

Bamboo filaments, 149. 
Bar magnets, 27; 

magnetic figures of, 38. 
Batteries, large plunge, 54; 

plunge, 53; 

secondary, 86; 

storage, and how they 
work. Chap. IX. 

169 



lyo 



THINGS A BOY SHOULD 



Bell, the electric, and some of 
its uses, Chap. XV.; 

electric, ii6; 

magneto testing, 117; 

trembling, etc., 116. 
Bell transmitter, 120. 
Belts, electricity generated by 

friction upon, j . 
Benjamin Franklin, 18. 
Bichromate of potash cells, 51, 

etc. 
Binding-posts, Chap. V.; 

common forms of, 63. 
Blasting, by electricity, 147; 

electric machines for, 147. 
Bluestone cell, 56. 
Boats, electric, 168. 
Boilers, use of in central sta- 
tions, 170. 
Bones, photographed by x- 

rays. Chap. XXIII. 
Boosters, 136. 
Brushes, 129. 
Bunsen cells, 56^. 
Burner, automatic, 174; 

for gas-lights, 174; 

ratchet, 174. 
Buzzers, electric, 118. 

Cables and wires, 143. 
Call boxes, electric, 173. 
Carbon, in arc lamps, 152, 153; 

filament, 149; 

transmitter, 123. 
Carpet, electricity generated 

upon, I. 
Cars, electric, 164; 

controllers for, 165; 

heating by electricity, 167; 

overhead system for, 166; 




underground system for, 
166. 
Cat, electricity generated upon, 

I. 
Cathode, definition of, 79; 

rays, 157. 
Cells, Bunsen, 560; 

bichromate of potash, 51; 

closed circuit, 50; 

dry, 58; 

Edison-Lelande, 59; 

electricity generated by. 
Chap. III.; 

Fuller, 55; 

Gonda, 57; 

gravity, 56; 

Grenet, 52; 

Leclanche, 57; 

open circuit, 50; 

plates and poles of, 45a; 

polarization of, 48; 

simple. 45, 49; 

single-fluid, 49; 

two-fluid, 49; 

various voltaic, Chap. IV. 
Central stations, 170; 

a word about. Chap. XXVI 
Chain lightning, 19. 
Chafing-dishes, electrical, 147. 
Charging condensers, 15. 
Chemical action, and electric- f 

ity, 81. 
Chemical effects of electric 

current. Chap. VII. 
Chemical meters, 78. 
Church organs, pumped by 

motors, 162. 
Circuits, electric, 50; 

for lamps, 144. 



ii 



ii 



KNOW ABOUT ELECTRICITY. 



171 



Cleats, porcelain, 141; 

wooden, 141. 
Clocks, automatic electric, 172. 
Closed circuit cells, 50. 
Coils, induction, and how they 
work, Chap. XIII.; 

induction, construction of, 
104; 

method of joining, 98; 

primary and secondary, 
103; 

resistance, 69; 

rotation of, 95; 

of transformers, 135. 
Collectors on dynamos, 129. 
Commutators, 129. 
Compasses, magnetic, 31. 
Compound, magnets, 28; 

wound dynamo, 131. 
Condensation of static electri- 
city, 15. 
Condensers, 15; 

for induction coils, 104. 
Conductors, and insulators, 4, 

138. 
Conduits, electric, 140. 
Connections, electrical, 60; 

for telegraph lines, iii. 
Controllers, for automobiles, 
169; 

for electric cars, 165. 
Copper sulphate, effects of 
current on, 82; 

formula of, 79. 
Copper voltameters, 75. 
Cords, adjustable for lamps, 

151. 
Coulomb, the, 76. 
Crater of hot carbons, 152. 
Crookes tubes, 156, 158. 



Current, detectors, 93; 

direction of in cell, 46; 
from magnet and coil, 100; 
from two coils, 102; 
induced, 127; 
of induction coils, 105; 
interrupters, automatic, 

104. 115; 
local, 47; 
primary and secondary, 

102; 
transformation of, Chap. 

XVIII. ; 
transmission of, 134. 
Currents, and motion, 160; 

how distributed for use. 
Chap. XIX. 
Current strength, 71; 
measurement of, 73; 
unit of, 72. 
Cylinder electric machines, 9. 

Daniell cell, 56. 

D'Arsonval galvanometer, 73. 

Declination, 41. 

Decorative incandescentlamps. 

151. 
Dental, lamps, 151; 

outfits, 176. 
Detectors, astatic, 94; 

current, 93. 
Diamagnetic bodies, 29. 
Diaphragm for telephones, 120. 
Dip, of magnetic needle, 42. 
Direct current, 129, 130. 
Direction of current in cell, 46. 
Discharging condensers, 15. 
Disruptive discharges, 154. 
Distribution of currents for 
use, Chap. XIX. 



172 



THINGS A BOY SHOUI^D 



Door opener, electric, 175. 

Dots and dashes, no. 

Drill press, run by motor, 162. 

Dry cells, 58. 

Dynamo, the, 126; 

alternating current, 130; 

commutator of, 129; 

compound wound, 131; 

direct current, 130; 

lamps connected to, 132; 

series wound, 131; 

shunt wound, 131 ; 

used as motor, 161; 

use of in central stations, 
170; 

used with water power, 170. 
Dynamos, electricity generated 
by. Chap. XVII.; 

types of, 130; 

various machines, 132; 

winding of, 131. 
Dynamotors, 137. 

Earth, inductive influence of, 

43; 

lines of force about, 40, 42. 
Ebonite, electricity by friction 

upon, 3, 4. 
Edison-Lelande cells, 59. 
Electric, automobiles, 169; 

beil, and some of its uses, 
Chap. XV.; 

boats, 168; 

buzzers, 118; 

cars, 164; 

conduits, 140; 

fans, 162; 

fiat-irons, 146; 

gas lighters, 174; 

griddles, 147; 



kitchen, 147; 

lights, arc, Chap. XXII.; 

lights, incandescent. Chap. 

XXL; 
machines, static. 7 to 13; 
machines, uses of, 14; 
motor, the, 161; 
motor, and how it does 

work. Chap. XXIV.; 
soldering irons, 146; 
telegraph, and how it 

sends messages. Chap. 

XIV.; 
telephone, and how it trans- 
mits speech. Chap. XVI.; 
welding, 146. 
Electric current, and work, 133; 
and chemical action, 81; 
chemical effects of. Chap. 

VII.; 
how distributed for use. 

Chap. XIX.; 
magnetic effects of. Chap. 

XL; 
how transformed, Chap. 

XVIII. 
Electrical, connections, 60; 
horse-power, 77; 
measurements. Chap. VI.; 
resistance, 68; 
resistance, unit of, 69; 
units. Chap. VL 
Electricity, about frictional, 

Chap. I. ; 
and chemical action, 81; 
atmospheric, 18; 
heat produced by. Chap. 

XX.; 
history of, 3; 
how generated upon cat, i; 



KNOW ABOUT ELECTRICITY. 



173 



how generated by dyna- 
mos, Chap. XVII. ; 
how generated by heat, 

Chap. X.; 
how generated by induc- 
tion, Chap. XII. ; 
how generated by voltaic 

cell. Chap. III.; 
origin of name, 2. 
Electrification, kinds of, 6; 

laws of, 7. 
Electrolysis, 79. 
Electrolyte, 79. 

Electromagnetic induction, 99. 
Electromagnetism, 91. 
Electromagnets, 96; 

forms of, 97. 
Electro-mechanical gong, 116. 
Electromotive force, defined, 

65, 71; 

measurement of, 67: 

of polarization, 85; 

of static electricity. 17; 

unit of, 66. 
Electrophorus, the, 8. 
Electroplating, 82. 
Electroscopes, 5. 
Electrotyping, 83. 
Experiments, early, with cur- 
rents, 44; 

some simple, r. 
External resistance, 68. 

Fan motors, 162. 
Field, magnetic, 37. 
Field-magnets, 129. 
Figures, magnetic, 38. 
Filaments, carbon, 149; 

bamboo, etc., 149. 
Fire, St. Elmo's, 22. 



Flat-irons, electric, 147. 
Floor mains, 139. 
Fluoroscope, 158. 
Force, and induced currents, 
loi; 

lines of magnetic, 38; 

lines of about a wire, 92, 

96; 

lines of about a magnet, 37, 
38. 
Frictional electricity, about, 
Chap, I. ; 

location of charge of, 4; 

sparks from, 4. 
Fuller cell, the, 55. 
Fuse, link, 142; 

plug, 142; 

ribbons, 142; 

wire, 142. 
Fusible rosettes, 142. 

Galvani, early experiments of, 

44. 
Galvanometers, 73; 

astatic, 73; 

considered as motor, 161; 

D'Arsonval, 73: 

tangent, 73. 
Galvanoscope, 73; 

astatic, 94. 
Gas lighters, electric, 174. 
Geissler tubes, 156. 
Generators, electric, 126. 
Glass, electricity generated 

upon, 4. 
Glue pots, electric, 147. 
Gold-leaf, for electroscopes, 5. 
Gold plating, 82. 
Gonda cell, 57. 
Gong, electro-mechanical, 116. 



174 



THINGS A BOY SHOULD 



Gravity cell, the, 56 ; 

replaced by dynamotors, 
137. 
Grenet cell, 52. 
Griddles, electric, 147. 
Guard, for lamps, 151. 

Heat, how generated by elec- 
tricity. Chap. X. ; 
and magnetism, 35; 
and resistance, 145. 
Heat lightning, 19. 
Heaters, for cars, 167. 
History of electricity, 3. 
Horse-power, electrical, 77. 
Horseshoe, permanent mag- 
nets, 26; 
electromagnets, 97, 98. 
Human body, bones of, photo- 
graphed by x-rays, 
Chap. XXIII. 
Hydrogen, action of in cell, 48; 
attraction of for oxygen, 
85. 

Incandescence, 148. 
Incandescent lamp, 149; 

candle-power of, 150; 

current for, 150; 

light produced by. Chap. 
XXL; 

construction of, 149; 

uses of, 151. 
Inclination of magnetic needle, 

42. 
Indicating push-button, 61. 
Induced currents, 127; 

and lines of force, loi; 

by rotary motion, 128; 

of induction coils, 105; 

of transformers, 135. 



Induced magnetism, 36. 
Induction, electricity generated 

by. Chap. XII.; 
electromagnetic, 99. 
Induction coils, condensers for, 

104; 

construction of, 104; 

currents of, 105; 

how they work, Chap. 

XIII.; 
in telephone work, 124; 
uses of, 106. 
Inductive influence of earth, 

43. 
Influence machines for medical 

purposes, 13. 
Ink writing registers, 114. 
Insulating tubing, 141. 
Insulators, 141; 

and conductors, 4, 138; 
feeder-wire, 167; 
for poles, 167; 
porcelain, 141. 
Internal resistance, 68. 
Interrupters, automatic cur- 
rent, 104, 115. 
Ions, 80. 

Iron, electricity upon, by fric- 
tion, 4. 

Jar, Leyden, 15. 

Jarring magnets, effects of, 33. 



Keeper of magnets, 26. 
Keys, telegraph, 109. 
Kinds of electrification, 6. 
Kitchen, electric, 147. 
Knife switch, 62. 



4 



Lamp, incandescent, 
power of, 150; 



candle- 



KNOW ABOUT ELECTRICITY. 



175 



cord, adjustable, 151; 

current for, 150; 

dental, 151; 

for desks, 151; 

for throat, 151; 

guard for, 151; 

incandescent, 149; 

socket, 151; 

with half shade, 151. 
Lamp, the arc, 153; 

how light is produced 
by, Chap. XXII.; 

double carbon, 153; 

hand-feed focussing, 153; 

for search-lights, 153; 

single carbon, 153; 

short, for basements, 153; 

for theater use, 153. 
Lamp circuits, alternating 

system, 14.4. 
Lamps, in parallel, 144; 

lamps in series, 144; 

three-wire system, 144; 

two-wire system, 144. 
Laws, of electrification, 7; 
^ of magnetic attraction, 32; 

of resistance, 70. 
Leaf electroscopes, 5. 
Leclanche cell, 57. 
Leyden, battery, 16; 

jar, 15. 

Light, how produced by arc 
lamp, Chap. XXIL; 
how produced by incan- 
descent lamp, Chap. 
XXI. 
Lightning, 19; 

rods, 21. 
Line, telegraph. Chap. XIV.; 
connections for, iii; 
operation of, 112. 



Line suspension, for trolley- 
wires, 167. 
Line wire, iii. 

Lines of force, conductors of, 
39. 96; 

about the earth, 40, 42; 

and induced currents, loi; 

about a magnet, 38; 

about a wire, 92. 
Local currents, 47. 

Magnetic, bodies, 29; 
declination, 41; 
effects of electric current. 

Chap. XL; 
field, 37; 
figure of one bar magnet, 

38; 

figure of two bar magnets, 

38; 

figure of horseshoe magnet, 

38; 

needle, dip of. 42; 

needles and compasses, 31. 
Magnetism, and heat, 35; 

induced, 36; 

laws of, 32; 

residual, 34; 

retentivity, 34; 

temporary, 36; 

terrestrial, 40; 

theory of, 33. 
Magneto, signal bells, 117; 

testing bells, 117; 

transmitter, 120. 
Magnets, action upon each 
other, 32; 

artificial, 25; 

bar, 27; 

compound, 28; 



176 



THINGS A BOY SHOULD 



effects of jarring, 33; 

electro, 96; 

electro, forms of, 97; 

horseshoe, 26; 

and magnetism, about, 
Chap. II.; 

making of, 30; 

natural, 24. 
Mains, electric, 139. 
Manholes, in conduits, 140. 
Measurements, electric. Chap. 
VI.; 

of current strength, 73; 

of E.M.F., 67. 
Meters, chemical, 78; 

permanent record, 77. 
Microphone, the, 122. 
Motion and currents, 160. 
Motor, acting like dynamo, 
163; 

armature of, 161 ; 

controlling speed of, 165; 

electric, 161; 

electric, and how it does 
work, Chap. XXIV.; 

fans, 162; 

for automobiles, 169; 

for boats, 168; 

for pumping bellows, 162; 

for running drill press, 162; 

parts of, 162; 

starting boxes for, 163; 

uses of, 162. 
Motor-dynamos, 136. 
Mouldings, for wires, 141. 

Name, electricity, origin of, 2. 
Natural magnets, 24. 
Needles, astatic, 94; 

dipping, 42; 

magnetic, 31. 



Negative electrification, 5. 
Non-conductors, 4. 
North pole, magnetic of earth, 
40; 
of magnets, 26. 
Northern lights, 23. 

Ohm, the, 69. 
Open circuit cells, 50. 
Openers, for doors, 175. 
Outfits, dental, 175. 
Overhead trolley system, 166. 
Oxygen, attraction for hydro- 
gen, 85. 

Parallel arrangement of lamps, 

144. 
Peltier effect, 89. 
Pendant, electric, 151. 
Pith-ball electroscope, 5. 
Plate electrical machine, 10. 
Plates of cells, 45a. 
Plunge batteries, 53; 

large, 54. 
Polarity of coils, 95. 
Polarization, 84; 

electromotive force of, 85; 

of cells, 48. 
Pole-changing switch, 62. 
Poles, of cells, 45^; 

of horseshoe magnet. 26. 
Positive electrification, 6. 
Potential, defined, 65. 
Push-buttons, Chap. V.; 

indicating, 61; 

modifications of, 61; 

table clamp, 61. 

Quantity of electricity, 76; 
unit of. 76. 



KNOW ABOUT ELECTRICITY. 



177 



Rays, cathode, 157; 

x-rays, 158. 
Receiver, telephone, 121. 
Reflectors, for lamps, 151. 
Registers, ink writing, 114. 
Relay, the, 113. 
Residual magnetism, 34. 
Resistance, coils and boxes. 
69; 

electrical, 68; 

external, 68; 

and heat, 145; 

internal, 68; 

laws of, 70; 

unit of, 69. 
Retentivity, 34. 
Risers, in buildings, 139. 
Rods, lightning: 21. 
Roentgen, Prof., 15S. 
Rosette, fusible, 142. 
Running-gear, of automobiles, 

169. 
Safety, devices, 142; 

fuse, 142: 

fuse link, 142; 

fuse plug, 142; 

fuse ribbon, 142; 

fuse wire, 142. 
Search-lights, 153; 

signals sent by, 153. 
Secondary batteries, 86; 

uses of, 87. 
Series arrangement of lamps, 

144- 
Series wound dynamo, 131. 
Service wires, 139. 
Shunt-wound dynamo, 131. 
Signal bells, magneto, 117. 
Simple cell, the, 45, 49. 
Single-fluid cells, 49. 



Single-point switch, 62. 
Single-stroke bell, 116. 
Socket, for incandescent lamps, 

151. 
Soldering irons, electric, 147. 
Sounders, telegraph, no; 

home-made, no. 
Spark, effect of air pressure on, 

155. 
Sparks, from cells, 17; 

from frictional electricity, 
4. 
St. Elmo's fire, 22. 
Starting boxes, for motors, 163. 
Static electric machines, 8. 
Static electricity, condensation 
of, 15; 

electromotive force of, 17; 

to test presence of, 5; 

uses of, 14. 
Steam engines, in central sta- 
tions, 170. 
Steel, inductive influence of 
earth upon^ 43; 

retentivity of, 26. 
Storage batteries, the, and how 
they work. Chap. IX.; 

for automobiles, 169; 

for boats, 16S; 

for natural sources of 
powder, 87. 
Stoves, electric, 147. 
Strength of current, 71; 

measurement of, 73; 

unit of, 72. 
. Switchboards, 62. 
Switches, Chap. V. ; 

knife, 62; 

pole-changing, 62; 

single point, 62: 

for trolley lines, 167. 



178 



THINGS A BOY SHOUI.D 



Table clamp-push, 6i. 
Tangent galvanometer, 73. 
Teakettles, electric, 147. 
Telegraph, electric, and how it 
sends messages, Chap. 
XIV.; 

ink writing registers, 114; 

keys, 109; 

relay, 113; 

sounders, no. 
Telegraph line, 107, 108; 

operation of, 112; 

simple connections of, in. 
Telephone, the, and how it 
transmits speech. Chap. 
XVI.; 

receiver, 121; 

transmitter, 120; 

use of induction coil with, 
124; 

various forms of, 125. 
Temporary magnetism, 36. 
Terrestrial magnetism, 40. 
Theory of magnetism, 33. 
Thermoelectricity, 88. 
Thermopiles, go. 
Three-wire system, 144. 
Throat, lamp for, 151. 
Thunder, 20. 

Toepler-Holtz machines, 11. 
Transformers, 135. 
Transforming electric current, 
Chap. XVIII.; 

for electric welding, 146. 
Transmission of currents, 134. 
Transmitter, Bell, 120; 

carbon, 123. 
Trembling bell, 116. 
Trolley-wires, 164; 

-poles, 164; 

-wheels, 164. 



Tubes, Crookes, 156, 158; 

Geissler, 156; 

vacuum, 156. 
Two-fluid cells, 49. 
Two-wire system, 144. 

Underground trolley system, 
166; 

conduits for, 166. 
Unit, of current strength, 72; 

of electromotive force, 66; 

of quantity, 76; 

of resistance, 69. 
Units, electrical. Chap. VI. 
Uses, of armatures, 39; 

of electricity, miscellane- 
ous, Chap. XXVII.; 

of induction coils, 106; 

of motors, 162; 

of storage batteries, 87. 

Vacuum-tubes, 156. 
Variation, angle of, 41. 
Volt, the, 66. 
Volta. 66; 

early experiments of, 44. 
Voltaic cell, electricity gen- 
erated by. Chap. III. 
Voltaic pile, 44. 
Voltameters, 75; 

copper, 75; 

water, 75. 
Voltmeters, 67, 77. 

Water, decomposition of, 79; 

power, source of energy, 
170; 

voltameters, 7j. 
Watt, the, 77. 
Wattmeters, 77. 
Welding, electric, 146. 



KNOW ABOUT ELECTRICITY. 



179 



Wimshurst electric machine, 

12. 
Wires and cables, 143. 
Wiring, for alternating system, 

144; 
three-wire system, 144; 
two-wire system, 144. 
Work, and electric current, 133. 



X-ray photographs, 159. 

X-rays, 156; 

and how the bones of the 
human body are photo- 
graphed. Chap. XXIII. 

Yokes, 97, 98. 

Zincs, amalgamation of, 47. 



Second Edition. 

How Two Boys Made Their Own 
Electrical Apparatus. 



Containing complete directions for making all kinds of simple 
electrical apparatus for the study of elementary electricity. By 
Professor Thomis M. St. Johx, Xew York City. 

The book measures 5 x Tj^ in., and is beautifully bound in 
cloth. It contains 141 pages and 125 illustrations. Complete 
directions are given for making 152 different pieces of Apparatus 
for the practical use of students, teachers, and others 'who wish 
to experiment. 

RRIOE, ROST-F^T^ID, $1.00. 



The shocking coils, telegraph instruments, batteries, electro- 
magnets, motors, etc., etc., are so simple in construction that any 
boy of average ability can make them; in fact, the illustrations 
have been made directly from apparatus constructed by young boys. 

The author has been working along this line for several years, and 
he has been able, icith the help of boys, to devise a complete line of 
simple electrical apparatus. 



THE APPARATUS IS SIMPLE because the designs atvd 

methods of constr^iction have been worked out prac- 

tically in the school-room, absolutely no viachine- 

work being required. 
THE APPARATUS IS PRACTICAL because it has been 

desigtied for real use in the experimental study of 

elementary electricity. 
THE APPARATUS IS CHEAP because most of the parts 

can be made of old tin caivsand cracker boxes, bolts, 

screws, wires atid wood. 



Address, THOMAS M. ST. JOHN, 

407 West 51st Street, 

New York. 



How Two Boys Made Their Own 
Electrical Apparatus. 



CONTENTS : Chapter I. Cells and Batteries— II. Battery Fluids and Solu- 
tions.— III. Miscellaneous Apparatus and Methods of Construction. —IV. 
Switches and Cut-Outs.— V. Binding-Posts and Connectors.— YI. Permanent 
Magnets —VII. Magnetic Needles and Compasses.— VIII. Yokes and Arma- 
tures.— IX. Electro-Magnets.— X. Wire-Winding Apparatus.— XL Induction 
Coils and Their Attachments.— XII. Contact Breakers and Current Inter- 
rupters.— XIII. Current Detectors and Galvanometers.— XIV. Telegraph Keys 
and Sounders.— XV. Electric Bells and Buzzers.— XVI. Commutators and Cur- 
rent Reversers.— XVII. Resistance Coils.— XVIII. Apparatus for Static Elec- 
tricity.— XTX. Electric Motors.— XX. OfldsflndE?idss. — XXT. Tools and Materials. 

"The author of this booiv is a icitcuci auvl wuier of great ingenuity, 
and we imagine that the effect of such a book as this falling into juvenile 
hands must be highly stimulating and beneticial. It is lull of explicit 
details and instructions in regard to a great variety of apparatus, and the 
materials required are all within the compass of very modest j)ocket- 
money. Moreover, it is systematic and entirely without rhetorical frills, 
so that the student can go right along without being diverted from good 
helpful work that will lead iiim to build useful apparatus and make him 
understand what he is about. The <lrawinii:s are plain and excellent. We 
heartily commend the book." — Electrical Engineer. 

''Those who visited the electrical exhibition last May cannot have 
failed to notice on the south gallery a very interesting exliibit, consisting, 
as it did, of electrical apparatus made by boys. The various devices there 
shown, comprising electro-magnets, telegraph keys and sounders, resist- 
ance coils, etc., were turned out by boys following the instructions given 
in the book with the above title, which is unquestionably one of the most 
practical little works yet written tliat treat of similar subjects, for with 
but a limited amount of mechanical knowledge, and by closely following 
the instructions given, almost any electrical device may be made at very 
small expense. That such a book fills a long-felt want may be inferred 
from the number of inquiries we are constantly receiving from persons 
desiring to make their own induction coils and other apparatus." — 
Electricity. 

" At the electrical show in New York last May one of the most inter- 
esting exhibits was that of simple electrical apparatus made by the boys 
in one of the private schools in the city. This apparatus, made by boys of 
thirteen to fifteen years of age, was from designs by the author of this 
clever little book, and it was remarkable to see what an ingenious use had 
been made of old tin tomato-cans, cracker-boxes, bolts, screws, wire, and 
wood. With these simple materials telegraph instruments, coils, buzzers, 
current detectors, motors, switches, armatures, and an almost endless 
variety of apparatus were made. In his book Mr. St. John has given 
directions in simple language for making and using these devices, and has 
illustrated these directions with admirable diagrams and cuts. The little 
volume is unique, and Avill prove exceedinorly helpful to those of our 
voung readers who are fortunate enough to possess themselves of a copy. 
For schools where a course of elementary science is taught, no better text- 
book in the first-steps in electricity is obtainable. "^2%e Oreat Jtound 



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St5 

^1 




The Study of Elementary Electricity and 
Magnetism by Experiment. 

By THOMAS M. ST* JOHN, Met. E. 

The book contains 220 pages and 168 illustrations; 
it measures 5^714 in- ^^d is bound in green cloth. 

This book is designed as a text-book for amateurs, 
students, and others who wish to take up a systematic 
course of elementary eledlrical experiments at home or in 
school. Full directions are given for 

Two Hundred Simple Experiments. 

The experiments are discussed by the author, after the 
student has been led to form his own opinion about the 
results obtained and the points learned. 

In seledling the apparatus for the experiments in this 
book, the author has kept constantly in mind the fadl 
that the average student will not buy the expensive 
pieces usually described in text-books. 

The two hundred, experiments given can be performed with 
simple apparatus; in fact, the student should make at least a part 
of his own apparatus, and for the benefit of those who wish to do 
this, the author has given, throughout the work, explanations 
that' will aid in the construction of certain pieces especially 
adapted to these experiments. For those who have the author's 
"How Two Boys Made Their Own Electrical Apparatus," con- 
stant references have been made to it as the " Apparatus Book," 
as this contains full details for making almost all kinds of simple 
apparatus needed in "The Study of Elementary Electricity and 
Magnetism by Experiment." 

If you wish to take up a systematic course of 
experiments — experiments that may be per- 
formed with simple, inexpensive apparatus, — 
this book will serve as a valuable guide. 



Fun With Magnetism^ 

BOOK AND COMPLETE OUTFIT FOR SIXTY- 
ONE EXPERIMENTS IN MAGNETISM . . . . 




Children like to do experiments; and in this way, better than in 
any other, a 'practical knowledge of the elern^ents of magnetism may be 
obtained. 

These experiments, although arranged to amuse boys and girls, 
have been found to be very useful in the class-room to supplement 
the ordinary exercises given in text-books of science. 

To secure the best possible qvality of apparatus, the horseshoe 
magnets were made at Sheffield, England, especially for these sets. 
They are new and strong. Other parts of the apparatus have also 
been selected and made with great care, to adapt them particularly 
to these experiments.— i^r(?w the author's preface. 

CONTENTS. — Experiments With Horseshoe Magnet. — Experiments 
With Magnetized Needles.— Experiments With Needles, Corks, Wires, Nails, 
etc.— Experiments With Bar Magnets.— Experiments With Floating Magnets. 
—Miscellaneous Experiments.— Miscellaneous Illustrations showing what very- 
small children can do with the Apparatus. — Diagrams showing how Magnetized 
Needles may be used by little children to make hundreds of pretty designs 
upon paper. 

AMUSING EXPERIMENTS— Something for Nervous People to 
Try.— The Jersey Mosquito.— The Stampede —The Runaway.— The Dog-fight. 
—The Whirligig.— The Naval Battle.— A String of Fish.— A Magnetic Gun.— A 
Top Upsidedown.— A Magnetic Windmill.— A Compass Upsidedown.— The 
Magnetic Acrobat.— The Busy Ant-hill.— The Magnetic Bridge.— The Merry-go- 
Round.— The Tight-rope Walker.— A Magnetic Motor Using Attractions and 
Repulsions. 

The Booh and Complete Out/it will be senty Post-paid, 
upon receipt of 35 Cents, by 

THOHAS M. ST. JOHN, 407 W. 51st St., New York. 



A Few Off = Hand Statements 



4 



that have been made about "Fun With Magnetism '* and "Fun With 
Electricity" in letters of inquiry to the author. (These statements 
were absolutely unsolicited .) 

** My little boy has your ' Fun With Magnetism' and enjoys it so 
much that if the * Fun With Electricity ' is ready I would like to 
have it for him. Please let me know," etc. 

'*I have had much fun with *Fun With Magnetism.' " 

"My boy has *Fun With Magnetism' and has enjoyed it very 
much and would like the other. Will you," etc. 

"Please let me know when * Fun With Electricity' is upon the 
market, for if it is as good as this, I shall certainly want it." 

'* I have just received ' Fim With Magnetism * and am delighted 
with it. Please send me 12 sets," etc. 

** I have * Fun With Magnetism ' and ' Fun With Electricity ' and 
have enjoyed them very much. Please send," etc. 

" I am much pleased with * Fun With Electricity' and would like 
to have," etc. 

*' * Fun With Electricity ' is fine and I have had lots of fun with it. 
Please send," etc. 

"Having experimented with both of your apparatus *Fun With 
Magnetism' and 'Fun With Electricity,' and having found them 
both amusing and instructive, I wish to ask," etc. 

" I have purchased your outfits * Fun With Electricity ' and * Pun 
With Magnetism,' and though they are designed for amusement, I 
find them a great help in my studies. Will you please," etc. 

"I have one of your outfits of *Fun With Electricity,* and I enjoy 
it very much, some of the experiments being very astonishing. 
Will you please," etc. 

" I have enjoyed * Fun With Magnetism ' and * Fun With Elec- 
tricity very much." 

"My little boy has your book *Fun With Electricity,' which has 
given him much amusement. He would like to have," etc. 

"I am very much pleased with both outfits. I am very much in 
favor of such things for boys ; it keeps ihem occupied with some- 
thing that is both amusing and instructive. Send me," etc. 



Fun With Electricity. 

BOOK AND COMPLETE OUTFIT FOR SIXTY 
EXPERIMENTS IN ELECTRICITY 




Enough of the principles of electricity are brought out to make 
the book instructive as well as amusing. The experiments are 
systematically arranged, and make a fascinating science course. No 
chemicals, no danger. 

The book is conversational and not at all ** schooly/' Harry and 
Ned being two boys who perform the experiments and talk over the 
results as they go along. 

**The book reads like a story." — '* An appropriate present for a 
boy or girl." — "Intelligent parents will appreciate ' Fun With Elec- 
tricity.'" — **Yery complete, because it contains both book and 
apparatus." — * There is no end to the fun which a boy or girl can 
have with this fascinating amusement." 

THERE IS FUN IN THESE EXPERIMENTS.-chain Light- 

ning.— An Electric Whirligig.— The Baby Thunderstorm.— A Race -with Elec- 
tricity.— An Electric Frog Pond.— An Electric Ding-Dong.— The Magic Finger. 
—Daddy Long-Legs.— Jumping Sally.— An Electric Kite.— Very Shocking.'— 
Condensed Lightning.— An Electric Fly-Trap. — The Merry Pendulum.— An 
Electric Ferry-Boat.— A Funny Piece of Paper.— A Joke on the Family Cat.— 
Electricity Plays Leap-Frog.— Lightning Goes Over a Bridge.— Electricity 
Carries a Lantern. — And 40 Others, 

The O TTTFIT contains 20 different articles. The B O OK OF INSTB ZTC- 

TION measures 5 x TJ^ inches, and has 38 illustrations, 55 pages, good paper 
and clear type. 



The Book and Complete Outfit will he sent, by mail or 
express, Charges Prepaid, upon receipt of 65 Cents, by 

THOMAS n. ST. JOHN, 407 W. 51st St., New York. 



Fun With Puzzles^ 



BOOK, KEY, AND COMPLETE OUTFIT FOR 
FOUR HUNDRED PUZZLES 



The BOOK measures 5x7>^ inches. It is well printed, nicely 
bound, and contains 15 chapters, 80 pages, and 128 illustrations. 
The KEY is illustrated. It is bound with the book, and con 
tains the solution of every puzzle. The COMPLETE OUTFIT 
is placed in a neat box with the book. It consis;:s of numbers, 
counters, figures, pictures, etc., for doing the puzzles. 

CONTENTS : Chapter (1) Secret Writing. (2) Magic Triangles, Squares, 
Rectangles, Hexagons, Crosses, Circles, etc. (3) Dropped Letter and Dropped 
Word Puzzles. (4) Mixed Proverbs, Prose and Rhyme. (5) Word Diamonds, 
Squares, Triangles, and Rhomboids. (G) Numerical Enigmas. (7) Jumbled 
Writing and Magic Proverbs. (8) Dissected Puzzles. (9) Hidden and Concealed 
Words. (10) Divided Cakes, Pies, Gardens, Farms, etc. (11) Bicycle and Boat 
Puzzles. (12) Various Word and Letter Puzzles. (13) Puzzles with Counters. 
(14) Combination Puzzles. (15) Mazes and Labyrinths. 

** Fun With Puzzles" is a book that every boy and girl should 
have. It is amusing, instructive, —educational. It is lust the thing 
to wake up boys and girls and make them think. They like it, 
because it is real fun. This sort of educational play should be given 
in every school-room and in every home. 

** Fun With Puzzles" will puzzle your friends, as well as yourself; 
it contains some real brain-splitters. Over 300 new and original 
puzzles are given, besides many that are hundreds of years old. 

Secret Writing. Among the many things that " F. W. P." con- 
tains, is the key to secret writing. It shows you a very simple way 
to write letters to your friends, and it is simply impossible for others 
to read what you have written, unless they know the secret. This, 
alone is a valuable thing for any boy or girl who wants to have 
some fun. 

The Book, Key, and Complete Outfit will he sent, postpaid, 
upon receipt of 35 cents, by 

TUOrXKS M. ST. JOHN, 407 West 51st St., New York City. 



Fun With Soap=Bubbles. 



BOOK AND COMPLETE 
BUBBLES AND FILMS . 



OUTFIT FOR FANCY 




THE OUTFIT contains everything necessary for thousands of beautiful 
bubbles and films. All highly colored articles have been carefully avoided, as 
cheap paints and dyes are positively dangerous in children's mouths. The 
outfit contains the following articles: 

One Book of Instructions, called *' Fun With Soap-Bubbles, " 1 Metal Base for 
Bubble Stand, 1 Wooden Rod for Bubble Stand, 3 Large Wire Rings for 
Bubble Stand, 1 Small Wire Ring, 3 Straws, 1 Package of Prepared Soap, 1 
Bubble Pipe, 1 Water-proof Bubble Horn. The complete outfit is placed in 
a neat box with the book. (Extra Horns, Soap, etc., furnished at slight cost.) 

CONTENTS OF BOOK.— Twenty-one Illustrations.— Introduction.— The 
Colors of Soap-bubbles.— The Outfit.— Soap Mixture.— Useful Hints.— Bubbles 
Blown With Pipes.— Bubbles Blown With Straws.— Bubbles Blown With 
the Horn.— Floating Bubbles.— Baby Bubbles.— Smoke Bubbles.— Bombshell 
Bubbles. — Dancing Bubbles. — Bubble Games —Supported Bubbles. — Bubble 
Cluster.— Suspended Bubbles.— Bubble Lamp Chimney.— Bubble Lenses. 
—Bubble Basket. —Bubble Bellows.— To Draw a Bubble Through a Ring. 
—Bubble Acorn.— Bubble Bottle.— A Bubble Within a Bubble.— Another 
Way.— Bubble Shade.— Bubble Hammock.— Wrestling Bubbles.— A Smoking 
Bubble.— Soap Films.— The Tennis Racket Film.— Fish-net Film.— Pan-shaped 
Film.— Bow and Arrow Film.— Bubble Dome.— Double Bubble Dome.— Pyra- 
mid Bubbles.— Turtle-back Bubbles.— Soap-bubbles and Frictional Electricity. 



*' There is nothing more beautiful than the airy-fairy soap-bubble with its 
everchanging colors." 



THE BEST POSSIBLE AMUSEMENT FOR OLD 
AND YOUNG. 



The BooTc and Complete Outfit will he sent, POST-PAID, 
upon receipt of 35 cents, by 

THOMAS n. ST. JOHN, 407 West 51st St., New York City, 



Dewey Flag Poles 

ARE LITTLE MODELS OF REAL 
FLAG POLES 

They are appropriate for any occasion, and 
suitable for any kind of decoration. They 
should stand on tables, mantels, pianos, etc. ; 
in fact, there is no better ornament for gen- 
eral use. 

"They should be in every home and in 
every school-room in the United States." 






*' No toy fort complete 
without a Dewey Flag 
Pole." 

"The children can fast- 
en them on the window- 
sill and watch them flutter 
by the hour." 
'* They hoist like big flags, at half-mast, etc." 
*' Invaluable for store- window decoration." 



• • • F=>RIOES • • • 

Small Size ; height 18 inches, fitted with 
United States or Cuban Silk Flag (4x6 in.) 
post-paid, 30c. 

Large Size : height 24 inches, fitted with 
United States Silk Flag (7x10 in.), post- 
paid, 40c. 

Large Size : fitted with Cuban or British Silk 
Flag (8x12 in.), post-paid, . . . 50c. 



DEWEY FLAG POLES are beautifully made 
of hard wood^ and fitted with best Silk FUigs. 



JINGO AND JINGO JUNIOR. 

Two Fascinating and Entirely Different 

Games, Played with One Outfit, and 

Complete in One Box. 




THIS HANDSOME) OUTFIT for playing the 
TWO GREAT WAR GAMES will be 
sent CHARGES PREPAID upon receipt of 
$i.oo. 
Address THOHAS M. ST. JOHN, 

407 West 51st Street, 

New York City. 



A Brand-New Idea in Games. 




•i 5&l;s or Steel. 



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>^ 



oVisfrea (r/ THOMAS M 5 




'A HUSTLE FBOM THE WORD GO.'> 

This Mxciting Game will be sent, Charges 
Prep.dd, by mail or express, upon receipt of 
65 Dents. 
Address THOflAS n. ST. JOHN, 

\ (A ^ ^ West 5 1 St Street, 




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